Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals:...

47
Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU ¨ LSMANN, OVE A. PETERS & PAUL M.H. DUMMER Preparation of root canal systems includes both enlargement and shaping of the complex endodontic space together with its disinfection. A variety of instruments and techniques have been developed and described for this critical stage of root canal treatment. Although many reports on root canal preparation can be found in the literature, definitive scientific evidence on the quality and clinical appropriateness of different instruments and techniques remains elusive. To a large extent this is because of methodological problems, making comparisons among different investigations difficult if not impossible. The first section of this paper discusses the main problems with the methodology of research relating to root canal preparation while the remaining section critically reviews current endodontic instruments and shaping techniques. Introduction Preparation of the root canal system is recognized as being one of the most important stages in root canal treatment (1, 2). It includes the removal of vital and necrotic tissues from the root canal system, along with infected root dentine and, in cases of retreatment, the removal of metallic and non-metallic obstacles. It aims to prepare the canal space to facilitate disinfection by irrigants and medicaments. Thus, canal preparation is the essential phase that eliminates infection. Prevention of reinfection is then achieved through the provision of a fluid-tight root canal filling and a coronal restoration. Although mechanical preparation and chemical disin- fection cannot be considered separately and are commonly referred to as chemomechanical or biome- chanical preparation the following review is intended to focus on the mechanical aspects of canal preparation cavity. Chemical disinfection by means of irrigation and medication will be reviewed separately in this issue. History of root canal preparation Although Fauchard (3), one of the founders of modern dentistry described instruments for trepanation of teeth, preparation of root canals and cauterization of pulps in his book ‘Le chirurgien dentiste’, no systematic description of preparation of the root canal system could be found in the literature at that time. In a survey of endodontic instrumentation up to 1800, Lilley (4) concluded, that at the end of the 18th century ‘ . . . only primitive hand instruments and excavators, some iron cauter instruments and only very few thin and flexible instruments for endodontic treatment had been available’. Indeed, Edward May- nard has been credited with the development of the first endodontic hand instruments. Notching a round wire (in the beginning watch springs, later piano wires) he created small needles for extirpation of pulp tissue (5, 6). In 1852 Arthur used small files for root canal enlargement (6–9). Textbooks in the middle of the 19th century recommended that root canals should be enlarged with broaches: ‘But the best method of forming these canals, is with a three- or four-sided broach, tapering to a sharp point, and its inclination corresponding as far as possible, with that of the fang. This instrument is employed to enlarge the canal, and give it a regular shape’ (10). In 1885 the Gates Glidden drill and in 1915 the K-file were introduced. Although standardization of instruments had been proposed in 30 Endodontic Topics 2005, 10, 30–76 All rights reserved Copyright r Blackwell Munksgaard ENDODONTIC TOPICS 2005 1601-1538

Transcript of Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals:...

Page 1: Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU¨ LSMANN, OVE A. PETERS & PAUL M.H.

Mechanical preparation of rootcanals: shaping goals, techniquesand meansMICHAEL HULSMANN, OVE A. PETERS & PAUL M.H. DUMMER

Preparation of root canal systems includes both enlargement and shaping of the complex endodontic space together

with its disinfection. A variety of instruments and techniques have been developed and described for this critical stage of

root canal treatment. Although many reports on root canal preparation can be found in the literature, definitive scientific

evidence on the quality and clinical appropriateness of different instruments and techniques remains elusive. To a large

extent this is because of methodological problems, making comparisons among different investigations difficult if not

impossible. The first section of this paper discusses the main problems with the methodology of research relating to root

canal preparation while the remaining section critically reviews current endodontic instruments and shaping techniques.

Introduction

Preparation of the root canal system is recognized as

being one of the most important stages in root canal

treatment (1, 2). It includes the removal of vital and

necrotic tissues from the root canal system, along with

infected root dentine and, in cases of retreatment, the

removal of metallic and non-metallic obstacles. It aims

to prepare the canal space to facilitate disinfection by

irrigants and medicaments. Thus, canal preparation is

the essential phase that eliminates infection. Prevention

of reinfection is then achieved through the provision of

a fluid-tight root canal filling and a coronal restoration.

Although mechanical preparation and chemical disin-

fection cannot be considered separately and are

commonly referred to as chemomechanical or biome-

chanical preparation the following review is intended to

focus on the mechanical aspects of canal preparation

cavity. Chemical disinfection by means of irrigation and

medication will be reviewed separately in this issue.

History of root canal preparation

Although Fauchard (3), one of the founders of modern

dentistry described instruments for trepanation of

teeth, preparation of root canals and cauterization of

pulps in his book ‘Le chirurgien dentiste’, no

systematic description of preparation of the root canal

system could be found in the literature at that time.

In a survey of endodontic instrumentation up to

1800, Lilley (4) concluded, that at the end of the 18th

century ‘ . . . only primitive hand instruments and

excavators, some iron cauter instruments and only very

few thin and flexible instruments for endodontic

treatment had been available’. Indeed, Edward May-

nard has been credited with the development of the

first endodontic hand instruments. Notching a round

wire (in the beginning watch springs, later piano wires)

he created small needles for extirpation of pulp tissue

(5, 6). In 1852 Arthur used small files for root canal

enlargement (6–9). Textbooks in the middle of the

19th century recommended that root canals should be

enlarged with broaches: ‘But the best method of

forming these canals, is with a three- or four-sided

broach, tapering to a sharp point, and its inclination

corresponding as far as possible, with that of the fang.

This instrument is employed to enlarge the canal, and

give it a regular shape’ (10). In 1885 the Gates Glidden

drill and in 1915 the K-file were introduced. Although

standardization of instruments had been proposed in

30

Endodontic Topics 2005, 10, 30–76All rights reserved

Copyright r Blackwell Munksgaard

ENDODONTIC TOPICS 20051601-1538

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1929 by Trebitsch and again by Ingle in 1958, ISO

specifications for endodontic instruments were not

published before 1974 (10).

The first description of the use of rotary devices seems

to have been by Oltramare (11). He reported the use of

fine needles with a rectangular cross-section, which

could be mounted into a dental handpiece. These

needles were passively introduced into the root canal to

the apical foramen and then the rotation started. He

claimed that usually the pulp stump was removed

immediately from the root canal and advocated the use

of only thin needles in curved root canals to avoid

instrument fractures. In 1889 William H. Rollins

developed the first endodontic handpiece for auto-

mated root canal preparation. He used specially

designed needles, which were mounted into a dental

handpiece with a 3601 rotation. To avoid instrument

fractures rotational speed was limited to 100 r.p.m.

(12). In the following years a variety of rotary systems

were developed and marketed using similar principles

(Fig. 1).

In 1928 the ‘Cursor filing contra-angle’ was devel-

oped by the Austrian company W&H (Burmoos,

Austria). This handpiece created a combined rotational

and vertical motion of the file (Fig. 2). Finally,

endodontic handpieces became popular in Europe with

the marketing of the Racer-handpiece (W&H) in 1958

(Fig. 3) and the Giromatic (MicroMega, Besancon,

France) in 1964. The Racer handpiece worked with a

vertical motion, the Giromatic with a reciprocal 901

rotation. Further endodontic handpieces such as the

Endolift (Kerr, Karlsruhe, Germany) with a combined

vertical and 901 rotational motion and similar devices

were marketed during this period of conventional

endodontic handpieces. All these devices worked with

limited, if any, rotation and/or a rigid up and down

motion of the instrument, which were all made from

stainless steel. The dentist could only influence the

rotational speed of the handpiece and the vertical

amplitude of the file movement by moving the hand-

piece (10, 13).

A period of modified endodontic handpieces began

with the introduction of the Canal Finder System (now

distributed by S.E.T., Grobenzell, Germany) by Levy

(14). The Canal Finder was the first endodontic

handpiece with a partially flexible motion. The

amplitude of the vertical file motion depended on the

rotary speed and the resistance of the file inside the root

canal and changed into a 901 rotational motion with

increasing resistance. It was an attempt to make the

root canal anatomy or at least the root canal diameter

one main influencing factor on the behaviour of the

instrument inside the canal. The Excalibur handpiece

(W&H) with laterally oscillating instruments or the

Fig. 1. Endodontic Beutelrock-bur in a handpiece with aflexible angle from 1912. Reprinted from (13) bypermission by Quintessence Verlag, Berlin.

Fig. 2. Cursor-handpiece (W&H) from 1928. Reprintedfrom (13) by permission by Quintessence.

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Endoplaner (Microna, Spreitenbach, Switzerland) with

an upward filing motion were further examples of

handpieces with modified working motions (10, 13).

Table 1 summarizes available instruments and hand-

pieces for engine-driven root canal preparation.

Richman (15) described the use of ultrasound in

endodontics but it was mainly the work of Martin &

Cunningham (16) in the 1970s that made ultrasonic

devices popular for root canal preparation. The first

ultrasonic device was marketed in 1980, the first sonic

device in 1984 (13). Since 1971 attempts have been

made to use laser devices for root canal preparation and

disinfection (17). Additionally, some non-instrumental

or electro-physical devices have been described such as

ionophoresis in several different versions, electrosurgi-

cal devices (Endox, Lysis, Munich, Germany) (18) or

the non-instrumental technique (NIT) of Lussi et al.

(19), using a vacuum pump for cleaning and filling of

root canals.

Instruments made from nickel–titanium (NiTi), first

described as hand instruments by Walia et al. (20), have

had a major impact on canal preparation. NiTi rotary

instruments introduced later use a 3601 rotation at low

speed and thus utilize methods and mechanical

principles described more than 100 years ago by

Rollins. While hand instruments continue to be used,

NiTi rotary instruments and advanced preparation

techniques offer new perspectives for root canal

preparation that have the potential to avoid some of

the major drawbacks of traditional instruments and

devices.

Goals of mechanical root canalpreparation

As stated earlier, mechanical instrumentation of the

root canal system is an important phase of root canal

preparation as it creates the space that allows irrigants

and antibacterial medicaments to more effectiveley

eradicate bacteria and eliminate bacterial byproducts.

However, it remains one of the most difficult tasks in

endodontic therapy.

In the literature various terms have been used for this

step of the treatment including instrumentation,

preparation, enlargement, and shaping.

The major goals of root canal preparation are the

prevention of periradicular disease and/or promotion

of healing in cases where disease already exists through:

� Removal of vital and necrotic tissue from the main

root canal(s).

� Creation of sufficient space for irrigation and

medication.

� Preservation of the integrity and location of the

apical canal anatomy.

� Avoidance of iatrogenic damage to the canal system

and root structure.

� Facilitation of canal filling.

� Avoidance of further irritation and/or infection of

the periradicular tissues.

� Preservation of sound root dentine to allow long-

term function of the tooth.

Techniques of root canal preparation include manual

preparation, automated root canal preparation, sonic

and ultrasonic preparation, use of laser systems, and

NITs.

Ingle (21) described the first formal root canal

preparation technique, which has become known as

the ‘standardized technique’. In this technique, each

Fig. 3. Racer-handpiece (W&H) from 1959. Reprintedfrom (13) by permission by Quintessence.

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Table 1. Summary of currently available systems for engine-driven systems for root canal preparation and theirrespecive properties

Handpiece Manufacturer Mode of action

Conventional systems

Racer Cardex, via W&H, Burmoos, Austria Vertical movement

Giromatic MicroMega, Besancon, France Reciprocal rotation (901)

Endo-Gripper Moyco Union Broach,

Montgomeryville, PA, USA

Reciprocal rotation (901)

Endolift Sybron Endo, Orange, CA, USA Vertical movement1reciprocal rotation (901)

Endolift M 4 Sybron Endo Reciprocal rotation (301)

Endocursor W&H Rotation (3601)

Intra-Endo 3 LD KaVo, Biberach, Germany Reciprocal rotation (901)

Alternator Unknown Reciprocal rotation (901)

Dynatrak Dentsply DeTrey, Konstanz, Germany Reciprocal rotation (901)

Flexible systems

Excalibur W&H Lateral oscillations

(2000 Hertz, 1.4–2 mm amplitude)

Endoplaner Microna, Spreitenbach, Switzerland Vertical motion1free rotation

Canal-Finder-System S.E.T., Grobenzell, Munich Vertical movement (0.3–1 mm)1free

rotation under friction

Canal-Leader 2000 S.E.T. Vertical movement (0.4–0.8 mm)1partial

rotation (20–301)

Intra-Endo 3-LDSY KaVo Vertical motion1free rotation

IMD 9GX HiTech, unknown 3601 – rotation with variable, torque-dependent

rotational speed (min 10/min)

Sonic systems

Sonic Air 3000 MicroMega

Endostar 5 Medidenta Int, Woodside, NY, USA 6000 Hz

Mecasonic MicroMega

MM 1400 Sonic Air MicroMega

Yoshida Rooty W&H 6000 Hz

MM 1500 Sonic Air MicroMega 1500–3000 Hz

Ultrasonic systems

Cavi-Endo Dentsply DeTrey Magnetostrictive 25 000 Hertz

Piezon Master EMS, Nyon, Switzerland Piezoceramic 25 000–32 000 Hz

ENAC OE 3 JD Osada, Tokyo, Japan Piezoceramic 30 000 Hz

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instrument was introduced to working length resulting

in a canal shape that matched the taper and size of the

final instrument. This technique was designed for

single-cone filling techniques.

Schilder (1) emphasized the need for thorough

cleaning of the root canal system, i.e., removal of all

organic contents of the entire root canal space with

instruments and abundant irrigation and coined the

axiom ‘what comes out is as important as what goes in’.

He stated that shaping must not only be carried out

with respect to the individual and unique anatomy of

each root canal but also in relation to the technique of

and material for final obturation. When gutta-percha

filling techniques were to be used he recommended

that the basic shape should be a continuously tapering

funnel following the shape of the original canal; this was

termed as the ‘concept of flow’ allowing both removal

of tissue and appropriate space for filling. Schilder

described five design objectives:

I. Continuously tapering funnel from the apex to the

access cavity.

II. Cross-sectional diameter should be narrower at

every point apically.

III. The root canal preparation should flow with the

shape of the original canal.

IV. The apical foramen should remain in its original

position.

V. The apical opening should be kept as small as

practical.

And four biologic objectives:

I. Confinement of instrumentation to the roots

themselves.

Table 1. Continued

Handpiece Manufacturer Mode of action

Piezotec PU 2000 Satelec, Merignac, France Piezoceramic 27 500 Hz

Odontoson Goof, Usser�d M�lle, Denmark Faret rod 42 000 Hz

Spacesonic 2000 Morita, Dietzenbach, Germany

NiTi systems

LightSpeed Lightspeed, San Antonio TX, USA Rotation (3601)

ProTaper Dentsply Maillefer, Ballaigues, Switzerland Rotation (3601)

K 3 Sybron Endo Rotation (3601)

ProFile 0.04 and 0.06 Dentsply Maillefer Rotation (3601), taper 0.4–0.8

Mity-Roto-Files Loser, Leverkusen, Germany Rotation (3601), taper 0.02

FlexMaster VDW, Munich Germany Rotation (3601), taper 0.02/0.04/0.05

RaCe FKG, La-Chaux De Fonds, Switzerland Rotation (3601)

Quantec SC, LX Tycom, now: Sybron Endo Rotation (3601)

EndoFlashn KaVo Rotation (3601)

NiTiTEE Loser Rotation (3601)

HERO 642 MicroMega Rotation (3601), taper 0.02–0.06

Tri Auto ZX Morita, Dietzenbach, Germany 3601-rotation1auto-reverse-mechanism and

integrated electrical length determination

GT Rotary Dentsply Maillefer Rotation (3601), taper 0.04–0.12

nInitially available as stainless-steel instruments.

Hulsmann et al.

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II. No forcing of necrotic debris beyond the foramen.

III. Removal of all tissue from the root canal space.

IV. Creation of sufficient space for intra-canal medica-

ments.

Challenges of root canal preparation

Anatomical factors

Several anatomical and histological studies have de-

monstrated the complexity of the anatomy of the root

canal system, including wide variations in the number,

length, curvature and diameter of root canals; the

complexity of the apical anatomy with accessory canals

and ramifications; communications between the canal

space and the lateral periodontium and the furcation

area; the anatomy of the peripheral root dentine

(22–25) (Fig. 4). This complex anatomy must be

regarded as one of the major challenges in root canal

preparation and is reviewed in detail elsewhere in this

issue.

Microbiological challenges

Both pulp tissue and root dentine may harbor

microorganisms and toxins (26–33). A detailed de-

scription of the complex microbiology of endodontic

infections lies beyond the scope of this review, this issue

recently has been reviewed by Ørstavik & PittFord

(34), Dahlen & Haapasalo (35), Spangberg & Haapa-

salo (36) and others.

Iatrogenic damage caused by rootcanal preparation

Weine et al. (37, 38) and Glickman & Dumsha (39)

have described the potential iatrogenic damage that can

occur to roots during preparation with conventional

steel instruments and included several distinct prepara-

tion errors:

Zip

Zipping of a root canal is the result of the tendency of

the instrument to straighten inside a curved root canal.

This results in over-enlargement of the canal along the

outer side of the curvature and under-preparation of

the inner aspect of the curvature at the apical end point.

The main axis of the root canal is transported, so that it

deviates from its original axis. Therefore, the terms

straightening, deviation, transportation are also used to

describe this type of irregular defect. The terms

‘teardrop’ and ‘hour-glass shape’ are used similarly to

describe the resulting shape of the zipped apical part of

the root canal (Fig. 5A, B).

Elbow

Creation of an ‘elbow’ is associated with zipping and

describes a narrow region of the root canal at the point

Fig. 4. Morphology of the apical parts of the root canalsystems of a maxillary pre-molar and canine as describedby Meyer (24). Reprinted from (13) by permission byQuintessence.

Fig. 5. (A, B) Simulated root canals in plastic blocksbefore and following preparation clearly demonstrate thegenesis of straightening and creation of zip and elbow.

Mechanical preparation of root canals

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of maximum curvature as a result of the irregular

widening that occurs coronally along the inner aspect

and apically along the outer aspect of the curve. The

irregular conicity and insufficient taper and flow

associated with elbow may jeopardize cleaning and

filling the apical part of the root canal (Fig. 6A, B).

Ledging

Ledging of the root canal may occur as a result of

preparation with inflexible instruments with a sharp,

inflexible cutting tip particularly when used in a

rotational motion. The ledge will be found on the

outer side of the curvature as a platform (Fig. 7), which

may be difficult to bypass as it frequently is associated

with blockage of the apical part of the root canal. The

occurrence of ledges was related to the degree of

curvature and design of instruments (40–42).

Perforation

Perforations of the root canal may occur as a result of

preparation with inflexible instruments with a sharp

cutting tip when used in a rotational motion (Fig. 8).

Perforations are associated with destruction of the root

cementum and irritation and/or infection of the

periodontal ligament and are difficult to seal. The

incidence of perforations in clinical treatment as well as

in experimental studies has been reported as ranging

from 2.5 to 10% (13, 43–46). A consecutive clinical

problem of perforations is that a part of the original

root canal will remain un- or underprepared if it is not

possible to regain access to the original root canal

apically of the perforation.

Strip perforation

Strip perforations result from over-preparation and

straightening along the inner aspect of the root canal

curvature (Fig. 9). These midroot perforations are

again associated with destruction of the root cementum

and irritation of the periodontal ligament and are

difficult to seal. The radicular walls to the furcal aspect

of roots are often extremely thin and were hence

termed ‘danger zones’.

Outer widening

First described by Bryant et al. (47) ‘outer widening’

describes an over-preparation and straightening along

Fig. 7. Ledging at the outer side of the root canalcurvature. Reprinted by permission of Quintessence.

Fig. 6. Elbow formation and apical zipping in a curvedmaxillary canine. Reprinted by permission from Urban &Fischer, Munich.

Hulsmann et al.

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the outer side of the curve without displacement of the

apical foramen. This phenomenon until now has been

detected only following preparation of simulated canals

in resin blocks.

Apical blockage

Apical blockage of the root canal occurs as a result of

packing of tissue or debris and results in a loss of

working length and of root canal patency (Fig. 10). As a

consequence complete disinfection of the most apical

part of the root canal system is impossible.

Damage to the apical foramen

Displacement and enlargement of the apical foramen

may occur as a result of incorrect determination of

working length, straightening of curved root canals,

over-extension and over-preparation. As a consequence

irritation of the periradicular tissues by extruded

irrigants or filling materials may occur because of the

loss of an apical stop. Clinical consequences of this

occurrence are reviewed elsewhere in this issue.

Besides these ‘classical’ preparation errors insufficient

taper (conicity) and flow as well as under- or over-

preparation and over- and underextension have been

mentioned in the literature.

Criteria for assessment of the qualityof root canal preparation

When analyzing the quality of root canal preparation

created by instruments and techniques several para-

meters are of special interest, particularly their cleaning

Fig. 8. Perforation of a curved root canal.

Fig. 9. Strip perforation at the inner side of thecurvature.

Fig. 10. Apical blockage by dentine debris. Reprintedwith kind permission from Quintessence, Berlin.

Mechanical preparation of root canals

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ability, their shaping ability as well as safety issues. A

detailed list of potential criteria for the assessment of

the quality of root canal instruments or preparation

techniques is presented in Table 2.

Methodological aspects in assessmentof preparation quality

Over recent decades a plethora of investigations on

manual and automated root canal preparation has been

published. Unfortunately, the results are partially

Table 2. Summary of possible criteria for assess-ment of techniques and instruments for root canalpreparation, including motors and handpieces

Disinfection

Reduction of the number of microorganisms

Removal of infected dentine

Improvement of irrigation

Unprepared areas

Cleanliness of root canal walls debris

Smear layer

Preparation shape

Longitudinal

Straightening, deviation

Displacement and enlargement of the apical foramen

Zips and elbows

Taper, conicity

Flow

Over/underextension

In cross-sections

Diameter

Circumferential/cross-sectional shape

Over/under-preparation

Fins and recesses

Increase in canal area

Danger of perforation into the furcation

Canal axis movement

Three-dimensional

Straightening and transportation

Changes in volume

Canal axis movement

Safety issues

Instrument fractures

Ledges

Perforations

Table 2. Continued

Excessive dentine removal

Apical blockage

Loss of working length

Extruded debris and/or irrigant

Temperature increase

Working time

Efficacy

Handling

Maintenance of digital/manual tactility

Adjustment of a stopper for length control

Insertion of instruments into handpiece

Programming the motor

Accessibility to the posterior region

Visualization during preparation

Assortment of files, quality of files, size designation

Integrated irrigation, type and amount of irrigant

Noise and vibrations of the handpiece or motor

Ergonomy and mobility of the device

Costs

Instruments

Motor or handpiece

Life-span of instruments and motor

Hulsmann et al.

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contradictory and no definite conclusions on the

usefulness of hand and/or rotary devices can be drawn,

Major deficiencies of studies on quality of root canal

preparation include:

� While currently available hand instruments have

been used for almost a century, no definitive mode

of use has emerged as the gold standard. However,

the Balanced force technique (48) may be cited as

such a gold standard for ex vivo and clinical studies

(49–51).

� In the majority of experimental studies published in

the literature only a small number of rotary systems

or rotary techniques are investigated and compared.

Only few studies include a comparison of four (39,

50, 52–56), five (57), or six and more (13, 45, 46,

58–65) devices and techniques.

� In the majority of these published studies only some

of the parameters listed in Table 2 were investigated,

thus allowing only limited conclusions on a certain

device, instrument or technique. The majority of

studies still focus on preparation shape in a long-

itudinal plane, whereas the number of studies on

cleaning ability remains small. This probably is

because of the fact, that the investigation of both

cleaning and shaping is difficult to perform in one

single experimental procedure and in any case

requires two different evaluations. Data on working

time and working safety are usually not collected in

separate experiments but rather are a side-product of

investigations designed for other purposes.

� A wide variety of experimental designs and metho-

dological considerations as well as of evaluation

criteria does not allow a comparison of the results of

different studies even when performed with the

same device or technique.

� Many publications do not include sufficient data on

sample composition, operator experience and train-

ing, calibration before assessment, e.g., photo-

graphs or electron micrographs, and on

reproducibility of the results (inter- and intra-

examiner agreement).

� It has been criticized that in many studies prepara-

tion protocols modified by the investigators have

been introduced and evaluated rather than the

preparation protocol as suggested by the manufac-

turer. This might result in inadequate use of

instruments and techniques and lead to misleading

results and conclusions.

Evaluation of post-operative rootcanal cleanliness

Post-operative root canal cleanliness has been investi-

gated histologically or under the SEM using long-

itudinal (13, 65, 66) and horizontal (67–69) sections of

extracted teeth. In horizontal sections remaining

predentine, pulpal tissue and debris may be stained

and the amount of remaining tissue and debris

measured quantitatively (68, 69). The use of horizontal

sections allows a good investigation of isthmuses and

recesses but loose debris inside the canal lumen may be

lost during sectioning. As well contamination of the

root canal system with dust from the saw blades may

occur.

The use of longitudinal sections allows nearly

complete inspection of both halves of the entire main

root canal. Lateral recesses and isthmuses are difficult to

observe. From a technical point of view it is difficult to

section a curved root, therefore it has been proposed

first to cut the root into horizontal segments which

then may be split longitudinally (13, 70). In horizontal

sections great care must be taken to avoid contamina-

tion during the sectioning process, which may be

prevented by insertion of a paper point or a gutta-

percha cone.

For the assessment of root canal cleanliness in the

majority of the studies two parameters have been

evaluated: debris and smear layer.

Debris may be defined as dentine chips, tissue

remnants and particles loosely attached to the root

canal wall.

Smear layer has been defined by the American

Association of Endodontists’ glossary ‘Contemporary

Terminology for Endodontics’ (71): A surface film of

debris retained on dentine or other surfaces after

instrumentation with either rotary instruments or

endodontic files; consists of dentine particles, remnants

of vital or necrotic pulp tissue, bacterial components

and retained irrigant.

Further criteria may be the reduction of bacteria and

the removal/presence of tissue, both of which are more

difficult to assess but clinically more relevant.

Scores

The standard technique for the evaluation of post-

operative root canal cleanliness is the investigation of

root segments under the SEM. For this purpose several

Mechanical preparation of root canals

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different protocols have been described. Some of these

studies are only of descriptive nature (53, 54, 72–75),

others use predefined scores. These scoring systems

include such with three scores (76–80), four scores (55,

64, 81–85), five scores (13, 65, 86–88), or even seven

scores (89). From the majority of these publications it

does not become clear, whether the specimens had

been coded and the examiner blinded before the SEM

investigation, preventing the identification of the

preparation instrument or technique under the SEM.

Furthermore, only in a few studies was the reproduci-

bility of the scoring described (65).

Additionally, the magnifications used under the SEM

differ widely, in some studies respective data are not

presented at all or different magnifications were used

during the investigation. A certain observer bias may

occur under the SEM when working with higher

magnifications, as only a small area of the root canal

wall can be observed. This area may be adjusted on the

screen by chance or be selected by the SEM operator. It

is a common finding that most SEM operators tend to

select clean canal areas with open dentinal tubules

rather than areas with large bulk of debris.

Not surprisingly, in most studies root canal cleanli-

ness has been demonstrated to be superior in the

coronal part of the root canal compared with the apical

part (13). Therefore an evaluation procedure specifying

the results for different parts of the root canal seems

preferable.

Evaluation of post-operative rootcanal shape

The aim of studies on post-operative root canal shape is

to evaluate the conicity, taper and flow, and main-

tenance of original canal shape, i.e., to record the

degree and frequency of straightening, apical transpor-

tation, ledging, zipping and the preparation of

teardrops and elbows as described by Weine et al. (37,

38). In the past investigations on post-operative root

canal shape have been performed using extracted teeth

or simulated root canals in resin blocks but this

parameter can be assessed clinically as well (90).

Simulated root canals in resin blocks

The several investigations on the shaping ability of

instruments and techniques for root canal preparation

have been performed using simulated root canals in

resin blocks (54, 91–106).

The use of simulated resin root canals allows

standardization of degree, location and radius of root

canal curvature in three dimensions as well as the

‘tissue’ hardness and the width of the root canals.

Techniques using superimposition of pre- and post-

operative root canal outlines can easily be applied to

these models thus facilitating measurement of devia-

tions at any point of the root canals using PC-based

measurement or subtraction radiography. This model

guarantees a high degree of reproducibility and

standardization of the experimental design. It has been

suggested that the results of such studies may be

transferred to human teeth (107–109).

Nevertheless, some concern has been expressed

regarding the differences in hardness between dentine

and resin. Microhardness of dentine has been measured

as 35–40 kg/mm2 near the pulp space, while the

hardness of resin materials used for simulated root

canals is estimated to range from 20 to 22 kg/mm2

depending on the material used (38, 110–112). For the

removal of natural dentine double the force had to be

applied than for resin (107). Additionally, it has been

criticized that the size of resin chips and natural dentine

chips may be not identical, resulting in frequent

blockages of the apical root canal space and difficulties

to remove the debris in resin canals (38, 107). In

consequence, data on working time and working safety

from studies using resin blocks may not be transferable

to the clinical situation.

Human teeth

The reproduction of the clinical situation may be

regarded as the major advantage of the use of extracted

human teeth, in particular when set-up in a manikin.

On the other hand, the wide range of variations in

three-dimensional root canal morphology makes stan-

dardization difficult. Variables include root canal length

and width, dentine hardness, irregular calcifications or

pulp stones, size and location of the apical constriction

and in particular angle, radius, length and location of

root canal curvatures including the three-dimensional

nature of curvatures.

Studies on post-operative root canal shape or changes

in root canal morphology, respectively, have been

performed in mesial root canals of mandibulary molars,

as these teeth in most cases show a curvature at least in

Hulsmann et al.

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the mesio-distal plane (113). Several techniques have

been developed to determine the characteristics of the

curvature, the most frequently used described by

Schneider (114). It measures the degree of the

curvature in order to categorize root canals as straight

(51 curvature or less), moderately (10–201) or severely

curved (4201). More advanced techniques (115–119)

aim to determine degree and radius as well as length

and location of the curve(s), since all of these factors

may influence the treatment/preparation outcome.

Early studies on preparation shape were conducted

using replica techniques (120–124), which are suited to

demonstrate post-operative taper and flow, smoothness

of root canal walls and quality of apical preparation. As

the original shape of the root canals remains unknown

the difference between pre- and post-operative shape

cannot be evaluated with such techniques.

Bramante et al. (125) were the first to develop a

method for the evaluation of changes in cross-sectional

root canal shapes. They imbedded extracted teeth in

acrylic resin blocks and constructed a plaster muffle

around this resin block. After sectioning the imbedded

teeth horizontally the resulting slices were reset into the

muffle for instrumentation. Pre- and post-instrumen-

tation photographs of the root canal diameter could be

superimposed and deviations between the two root

canal outlines could be measured. Subsequently,

improved versions of the ‘Bramante technique’ were

descibed (66, 126–130). The quantification of post-

operative root canal deviation may be performed using

the ‘centring ratio’ method (126, 131–134) or via

measurement of the pre- and post-operative dentine

thickness (135). This method also allows evaluation of

circular removal of predentine and cleanliness of

isthmuses and recesses (136, 137).

Recent technologies include the use of high-resolu-

tion tomography and micro-computed tomography

(CT) (50, 138–143). This non-destructive technique

allows measurement of changes in canal volume and

surface area as well as differences between pre- and

post-preparation root canal anatomy. The advantages

of these techniques are three-dimensional replication of

the root canal system, the possibility of repeated

measurements (pre-, intra- and post-operative) and

the computer aided measurement of differences

between two images. The use of micro-CT additionally

enables the evaluation of the extent of unprepared canal

surface and of canal transportation in three dimensions

(Fig. 11).

Apical extrusion of debris

Measurements of the amount of debris extruded

apically through the apical constriction were mostly

conducted by collecting and weighing this material

during preparation of extracted teeth (13, 70, 144–

154). It must be noted that such techniques are

unreliable for several reasons: working on extracted

teeth there is no resistance from the periradicular

tissues preventing the flow of irrigants through the

foramen. The way the debris is collected and drying and

weighing procedures also may have some (unknown)

influence on the results. The results from the various

studies, some of which were conducted without

irrigation during preparation, show a wide range of

results from 0.01 mg to 1.3 g (13). Moreover, Fair-

bourn et al. (145) reported an extrusion of 0.3 mg

during hand filing to a size #35 including irrigation,

while Myers & Montgomery (148) found extrusion of

0.01–0.69 mg during hand filing to size #40 including

irrigation.

From these studies it can be concluded that it is

unlikely to prepare a root canal system chemo-

mechanically without any extrusion of debris (44).

The amount of extruded debris probably depends on

the apical extent of preparation (144, 148). As it is not

known to which degree the extruded material is

infected and which amount is tolerated by the periapical

tissues, the clinical relevance of such data must remain

questionable. Phagocytosis of small amounts of debris

has been reported (155–157); however, extruded

material has been held responsible for post-operative

flare-ups and bacteraemia (158–160).

Evaluation of safety issues

The main safety issues reported in studies on root canal

preparation concern instrument fractures, apical

blockages, loss of working length, ledging, perfora-

tions, rise of temperature, and apical extrusion of

debris. Most of these issues have not been investigated

systematically in specially designed investigations.

In some retrospective evaluations of endodontically

treated teeth an incidence of instrument separation in

2–6% of the cases has been reported (161–165).

Instrument fractures may be related to the type, design

and quality of the instruments used, the material they

are manufactured from, rotational speed and torque,

pressure and deflection during preparation, the angle

Mechanical preparation of root canals

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and radius of the root canal curvature, frequency of use,

sterilization technique and probably various other

factors, in particular the operators’ level of expertise.

No systematic investigations of instrument fracture

of conventional steel instruments or conventional

automated devices could be found in the literature,

but because of their design Hedstrom files seem to

be more prone to fracture than other instruments

(166–168). A high number of fractures were reported

in ex vivo studies of rotary NiTi instruments but the

clinical incidence of such fractures has not yet been

investigated.

Evaluation of working time

The aim of the evaluation of working time for any

instrument or technique is to draw conclusions on the

Fig. 11. Three root canal preparation techniques (columns A–C) analysed by micro-CT. Reconstruction of three-dimensional canal models (rows 1, 3, 4 and cross-sections (row 2) with pre-operative canals in green and postoperativeshapes in red. Reprinted from (327) by permission of the Journal of Endodontics (30: 569, 2004).

Hulsmann et al.

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efficacy of the device or technique and on its clinical

suitability. Data on working time show large differences

for identical instruments and techniques, which is

because of methodological problems as well as to

individual factors.

Therefore, data from different studies should be

compared with caution, as variation caused by indivi-

duals (169) cannot be defined exactly but should be

regarded as decisive in many cases. For example, it was

demonstrated that instrument fractures resulted in

longer working times for the following instruments in

order to avoid additional fractures (170, 171).

For the evaluation of the efficacy of an instrument the

measurement of the cutting ability therefore seems to

more appropriate (172, 173). Theses studies use an

electric motor driving the root canal instrument into

natural root canals in extracted teeth or artificial canals

in resin blocks, thus excluding individual factors.

However, this does not exactly mirror the clinical

situation either.

In the recent past four major series of standardized

comparative investigations on rotary NiTi instruments

have been published. These will be briefly reviewed.

The Cardiff experimental design

This series of investigations (97–106, 174–177) was

performed in simulated root canals. Four types of root

canals were constructed using size #20 silver points as

templates. The silver points were pre-curved with the

aid of a canal former, to form four different canal types

in terms of angle and location. The four canal types

were:

Curvature 201, beginning of the curvature 8 mm from

the orifice.

Curvature 401, beginning of the curvature 12 mm from

the orifice.

Curvature 201, beginning of the curvature 8 mm from

the orifice.

Curvature 401, beginning of the curvature 12 mm from

the orifice.

The following variables and events were recorded and

evaluated: preparation time, instrument failure (defor-

mation and fracture), canal blockage, loss of working

distance, transportation, canal form (apical stop,

smoothness, taper and flow, aberrations (zips, elbows,

ledges, perforations, danger zones), canal width.

The Zurich experimental design

In a series of investigations (50, 138–143) the Zurich

group used high-resolution or micro-CT to measure

changes in canal volume and surface area as well as

differences between pre- and post-preparation root

canal anatomy. The advantages of this non-destructive

technique are three-dimensional replication of the root

canal system, the possibility of repeated measurements

(pre-, intra- and post-operative), and the computer-

aided measurement of differences between two images.

The use of micro-CT enables the evaluation of changes

in volume and surface area of the root canal system, the

extent of unprepared canal surface and canal transpor-

tation in three dimensions (Fig. 11). Similar experi-

ments by other groups have since corroborated and

expanded the findings cited above.

In this system, maxillary molars are embedded into

resin and mounted on SEM stubs, in order to allow

reproducible positioning into the micro-CT. This

approach in conjunction with specific software renders

high reproducibility (139) and allows comparisons of

pre- and post-operative canal shapes with accuracy

approaching the voxel size (currently 18–36 mm).

Specimens are then further characterized with respect

to pre-operative canal anatomy (volume, curvature)

and divided into statistically similar experimental

groups. Analyses can then be carried out with software

that separates virtual root canals, automatically detects

the canal axis and its changes after preparation and the

amount of preparared root canal surface area.

The Gottingen experimental design

This series of investigations (13, 91, 92, 137, 170, 171,

178–183) on conventional endodontic handpieces as

well as on several rotary NiTi systems made use of a

modified version of Bramante’s muffle model (125).

A muffle block is used allowing removal and exact

repositioning of the complete specimen or sectioned

parts of it. A modification of a radiographic platform, as

described by Sydney et al. (184) and Southard et al.

(185), may be adjusted to the outsides of the middle

part of the muffle. This allows radiographs to be taken

under standardized conditions, so that these radio-

graphs, taken before, during and after root canal

preparation may be superimposed. A pre-fabricated

stainless-steel crown may be inserted at the bottom of

Mechanical preparation of root canals

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the middle part of the muffle system to collect apically

extruded debris (Fig. 12A, B).

After embedding, mesio-buccal canals of extracted

mandibular molars with two separate patent mesial

root canals are prepared. Root canal straightening,

working time and working safety are recorded by

superimposition of radiographs taken under standar-

dized conditions. Following this the tooth block is

separated into four parts with a saw, the crown and

three segments with the roots. After taking standar-

dized photographs of the pre-operative cross-section of

the mesio-lingual root canal this is prepared. Again

photographs of the cross-section are taken, allowing

superimposition of both pre- and post-operative canal

circumference and evaluation of changes in cross-

section. Additionally, the percentage of unprepared

root canal wall areas can be measured. Again working

time and procedural incidents are recorded. The three

root segments finally are split longitudinally and the

cleanliness of the root canal walls is evaluated under

SEM using five scores for separate evaluation of

remaining debris (magnification � 200) and smear

layer (� 1000) (65).

While Bramante et al. (125) originally intended

to evaluate changes in cross-sectional diameter, this

model allows the parallel investigation of several

important parameters of root canal preparation:

straightening in the longitudinal axis, changes in root

canal diameter (horizontal), root canal cleanliness,

working time, and safety issues. Initially, an attempt

was made to collect and weigh the apically extruded

debris too, but this part of the model produced

unreliable results. Shortcomings of this model are

related mainly to the irregularities in human root canal

anatomy and morphology.

The Munster experimental design

This recent series of investigations on several rotary

NiTi systems (186–194) uses two types of plastic blocks

with different degrees of curvature (281 and 351) for

the evaluation of straightening and working safety as

well as extracted teeth with severely curved root canals

(25–351) for the evaluation of root canal cleanliness,

working safety and working time.

Manual preparation techniques

Several different instrumentation techniques have been

described in the literature, a summary of some more

popular techniques is presented in Table 3. Some of

these techniques use specially designed instruments

(e.g., the Balanced force technique was described for

Flex-R instruments).

Fig. 12. (a, b) Parts of the muffle system from the Gottingen studies (a–c). After removal of the outer parts of the mufflesystem a film holder (a) and a holder for reproducible attachment of the X-ray beam (c) can be adjusted to the middle partof the muffle (b) containing the prepared tooth. Two metal wire are integrated into the film holder, allowing exactsuperimposition of the radiograph (arrows).

Hulsmann et al.

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Manual preparation techniques andresults of studies

Balanced force technique

This technique, reported by Roane & Sabala in 1985

(48, 202), was originally associated with specially

designed stainless-steel or NiTi K-type instruments

(Flex-R-Files) with modified tips in a stepdown

manner. Instruments are introduced into the root

canal with a clockwise motion of maximum 1801 and

apical advancement (placement phase), followed by a

counterclockwise rotation of maximum 1201 with

adequate apical pressure (cutting phase). The final

removal phase is then performed with a clockwise

rotation and withdrawal of the file from the root canal.

Apical preparation is recommended to larger sizes than

with other manual techniques, e.g., to size #80 in

straight canals and #45 in curved canals. The main

advantages of the Balanced force technique are good

apical control of the file tip as the instrument does not

cut over the complete length, good centring of the

instrument because of the non-cutting safety tip, and

no need to pre-curve the instrument (2).

Roane & Sabala (48) themselves and further studies

(49, 50, 131, 185, 203, 207, 208, 213–217) described

good results for the preparation of curved canals

without or with only minimal straightening. However,

others reported a relatively high incidence of procedur-

al problems such as root perforations (218) or

instrument fractures (219). The amount of apically

extruded debris was less than with stepback or

ultrasonic techniques (147, 150, 220), the apical

region showed good cleanliness (221). Varying results

were reported for the amount of dentine removed; in

one study the Balanced force technique performed

superior compared with the stepback technique (126),

while in another study more dentine was removed

1 mm from the apex when using the stepback technique

(222). When used in a double-flared sequence canal

Table 3. Summary of manual root canal preparation techniques described in the literature

Approach Author(s) References

Standardized technique Ingle (1961) (21)

Step-back technique Clem (1969) (195)

Circumferential filing Lim & Stock (1987) (196)

Incremental technique Weine et al. (1970) (197)

Anticurvature filing Abou-Rass et al. (1980) (198)

Step-down technique Marshall & Papin (1980) (199)

Step-down technique Goerig et al. (1982) (200)

Double flare technique Fava (1983) (201)

Crown-down-pressureless technique Morgan & Montgomery (1984) (123)

Balanced force technique Roane et al. (1985) (48, 202)

Canal Master technique Wildey & Senia (1989) (204, 205)

Apical box technique Tronstad (1991) (206)

Progressive enlargement technique Backman et al. (1992) (207)

Modified double flare technique Saunders & Saunders (1992) (208)

Passive stepback technique Torabinejad (1994) (209, 210)

Alternated rotary motions-technique (ARM) Siqueira et al. (2002) (211)

Apical patency technique Buchanan (1989) (212)

Mechanical preparation of root canals

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area after shaping was larger than after preparation with

Flexogates or Canal Master U-instruments (223).

Post-instrumentation area was also greater in com-

parison with Lightspeed preparation (224), following

ultrasonic preparation or rotary Canal Master prepara-

tion and equal to hand preparation using the stepback

technique (49). A comparison of NiTi K-files used in

Balanced forces motion to current rotary instrument

systems indicated similar shaping abilities (50). How-

ever, some earlier reports had indicated significantly

more displacement of the root canal centres, suggesting

straightening (224, 225).

Cleanliness was rated superior compared with the

crowndown pressureless and stepback techniques (76).

The Balanced force technique required more working

time than preparation with GT Rotary, Lightspeed or

ProFile NiTi instruments (217, 225).

Stepback vs. stepdown

Stepback and stepdown techniques for long have been

the two major approaches to shaping and cleaning

procedures. Serial, telescopic or stepback techniques

commence preparation at the apex with small instru-

ments. Following apical enlargement instrumentation

length may be reduced with increasing instrument size.

Stepdown techniques commence preparation using

larger instrument sizes at the canal orifice, working

down the root canal with progressively smaller instru-

ments. Major goals of crowndown techniques are

reduction of periapically extruded necrotic debris and

minimization of root canal straightening. Since during

the stepdown there is less constraint to the files and

better control of the file tip it has been expected

that apical zipping is less likely to occur. Over the

years several modifications of these techniques have

been proposed, such as the crowndown technique, as

well as hybrid techniques combining an initial step-

down with a subsequent stepback (modified double

flare) (Table 3).

Although stepback and stepdown techniques may be

regarded as the traditional manual preparation techni-

ques there are surprisingly few comparative studies on

these two techniques. There is no definite proof that

‘classical’ stepdown techniques are superior to stepback

techniques. Only the Balanced force technique, which

is a stepdown technique as well, has been shown to

result in less straightening than stepback or standar-

dized techniques (126, 207, 219).

In a comparative study of four preparation techniques

no difference between stepback and crowndown was

detected in terms of straightening, but crowndown

produced more ledges (117). Using the Balanced force

technique, the apical part of curved root canals showed

less residual debris than following preparation with the

crowndown pressureless or stepback technique (76)

although stepback preparation resulted in a larger

increase in canal diameter and more dentine removal

than Balanced force preparation (222).

Crowndown techniques have been reported to

produce less apically extruded debris than stepback

preparation (146, 147, 152, 216).

Conventional rotary systems

In an extensive series of experiments the Gottingen

group compared preparation quality, cleaning ability

and working safety of different conventional endodon-

tic handpieces (13). The study involved a total of 15

groups each with 15 prepared teeth. Devices and

techniques evaluated included the Giromatic with two

different files, Endolift, Endocursor, Canal-Leader with

two different files, Canal-Finder with two different files,

Intra-Endo 3-LDSY, manual preparation, Excalibur,

Endoplaner, Ultrasonics and the Rotofile NiTi instru-

ments (in other countries known as MiTy-Roto-Files).

Mean root canal curvature of the different groups in

this study was between 17.81 and 25.11, all root canals

were enlarged to size #35. Further studies were

performed on the Excalibur (226) and the Endoplaner.

Taken together, these studies demonstrated that

preparation of curved root canals using conventional

automated devices with stainless-steel instruments in

many cases resulted in severe straightening. Similar

results earlier already had been found in studies on the

� Endolift (13, 52, 54, 63).

� Endolift M4 (227, 228).

� Endocursor (39, 122, 229).

� Excalibur (45, 46, 63, 226, 230–231).

� EndoGripper (228).

� Intra-Endo 3-LDSY (45, 46, 63, 232).

� Endoplaner (63).

� Giromatic (39, 52, 54, 70, 122, 233–238).

� Canal-Finder System (13, 54, 63, 72, 74, 85, 92,

128, 239–241). In some studies the Canal-Finder

straightened less than or equal to hand instrumenta-

tion (59, 242–244).

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� Canal-Leader (13, 241, 245, 246).

� Ultrasonics (13, 53, 54, 59, 241, 247–254).

Few studies have been published on post-operative

root canal cleanliness after preparation with the devices

mentioned above. The majority of these reported on

large agglomerations of debris and smear layer covering

almost the complete root canal wall (54, 61, 64, 64, 85,

230, 232, 255). In some studies slightly superior

results were found for automated systems with

integrated water supply, for example the Canal Finder

and the Canal Leader (65, 75, 256).

Additionally, for some of the automated devices severe

problems concerning safety issues (apical blockages, loss

of working length, perforations and instrument frac-

tures) have been reported (13, 54, 58, 59, 63, 94, 110,

111, 152, 226, 227, 230, 237, 243, 257–263).

NiTi systems

Metallurgical aspects

Several metallurgical aspects of NiTi instruments have

been extensively reviewed previously (264–266). Two

of the main characteristics of this alloy, composed of

approximately 55% (wt) nickel and 45% (wt) titanium

are memory shape and superior elasticity. The elastic

limit in bending and torsion is two to three times higher

than that of steel instruments. The modulus of elasticity

is significantly lower for NiTi alloys than for steel,

therefore much lower forces are exerted on radicular

wall dentine, compared with steel instruments. These

unique properties are related to the fact that NiTi is a

so-called ‘shape memory alloy’, existing in two

different crystalline forms: austenite and martensite.

The austenitic phase transforms into the martensitic

phase on stressing at a constant temperature and in this

form needs only light force for bending. After release of

stresses the metal returns into the austenitic phase and

the file regains its original shape. Because of the metallic

properties of NiTi, it became possible to engineer

instruments with greater tapers than 2%, which is the

norm for steel instruments (266).

Instrument designs

Over the years several different NiTi systems have been

designed and introduced on the market (see Table 1).

This review does not aim at a detailed presentation,

description and analysis of specific instrument designs,

but it should be kept in mind that design features such

as cutting angle, number of blades, tip design, conicity

and cross-section, will influence the instruments’

flexibility, cutting efficacy, and torsional resistance.

Design and clinical usage of some of these NiTi systems

are described in detail elsewhere in this issue.

Motor systems

Initially, NiTi instruments were used in regular low-

speed dental handpieces, which resulted in a clinically

unacceptable number of instrument fractures. In

consequence, special motors with constant speed and

constant torque were introduced for use with these

instruments (Table 4). Earlier concepts preferring

high-torque motors were followed by development of

low-torque motors, some of which have several special

features as auto start/stop, auto apical reverse in

combination with an electronic device for determina-

tion of working length, auto torque stop, auto torque

reverse, handpiece calibration, twisting motion and

programmed file sequences for primary preparation

and retreatment.

Initially, high-torque motors were preferred in order

to allow efficient cutting of dentine and to prevent

locking of the instrument. However, the incidence of

instrument fractures was relatively high with these

motors. The rationale for the use of low-torque or

controlled-torque motors with individually adjusted

torque limits for each individual file is to keep the

instrument working below the limit of instrument

elasticity without exceeding the instrument-specific

torque limit thus reducing the risk of instrument

fracture (267). The values should range between the

martensitic start clinical stress and the martensitic finish

clinical stress, which is dependent on design and taper

of the individual instrument.

On the other hand, current norms stipulate the

measurement of torque at failure at D3, a distance of

3 mm from the tip of the instrument. For an instrument

with a taper of 0.06 and larger, it becomes difficult to

determine a torque that is sufficient to rotate the larger

more coronal part of the instrument efficiently while

not endangering the more fragile apical part. In fact, it

has been suggested repeatedly that the creation of a

glide path allows the apical end of the instrument to act

as a passive pilot and thus protects the instrument from

breakage even with high torque.

Mechanical preparation of root canals

47

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Tab

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lues

:1

0/

20

/3

5/

45

/5

5N

cmA

llsy

stem

s

No

uva

gT

CM

En

do

Nou

vag

Lo

wto

rque

1.0

Ncm

,-(

no

lim

it)-

All

syst

ems

No

uva

gT

CM

En

do

Vn

Nou

vag

Lo

wto

rque

10

valu

es:0.2

–5.0

Ncm

All

syst

ems

En

do

Ste

pper

Ko

met

,L

emgo

,G

erm

any

Rig

ht

torq

ue

Ind

ivid

ual

for

any

file

All

syst

ems

ITco

ntr

ol

VD

WR

igh

tto

rqu

eIn

div

idu

alfo

ran

yfile

All

syst

ems

E-m

aste

rV

DW

Rig

ht

torq

ue

Indiv

idual

for

any

file

;10

valu

es:0.2

–3.0

Ncm

Only

Fle

xMas

ter

AT

RT

ecnik

aD

ents

ply

,L

aP

isto

ia,It

aly,

Low

torq

ue

Indiv

idual

for

any

file

All

syst

ems

K3-e

tcm

Ker

r,K

arls

ruhe,

Ger

man

yL

ow

torq

ue

5va

lues

:o

0.5

,o

0.9

,1

.2,

1.7

,2

.0N

cmK

3

Su

rgim

oto

rII

IA

septi

co,

Wo

odvi

lle,

NJ,

USA

5va

lues

All

syst

ems

Quan

tec

ET

MSyb

ron

Endo

Quan

tec,

K3

Tri

Au

toZ

Xn

Mo

rita

,T

oki

o,

Japan

Lo

wto

rque

7va

lues

All

syst

ems

Den

taport

nM

ori

ta,

To

kio

,Ja

pan

Lo

wto

rque

11

valu

esA

llsy

stem

s

EN

DO

flas

hK

aVo

Lo

wto

rque

3va

lues

:0

.05

,0

.09,

0.1

4N

cmA

llsy

stem

s

EN

DO

adva

nce

KaV

oL

ow

torq

ue

4va

lues

:0

.25

,0

.5,1

.0,

3.0

Ncm

All

syst

ems

Anth

ogyr

-han

dpie

ceD

ents

ply

,B

alla

igues

,Sw

itze

rlan

dL

ow

torq

ue

4va

lues

:o

1,

1,2

.25

,o

4.5

Ncm

All

syst

ems

En

dy

50

00n

Ion

yx,B

lan

qu

efort

,F

ran

ceL

ow

torq

ue

All

syst

ems

Endo-M

ate

TC

NSK

Euro

pe,

Fra

nkf

urt

,G

erm

any,

Low

torq

ue

6va

lues

:0.7

,1.5

,2.3

,3.0

,3.7

,4.5

Ncm

All

syst

ems

Tas

cal-

han

dpie

ceM

ax-D

enta

l,A

ugsb

urg

,G

erm

any

Undefi

ned

Han

dpie

cefo

rpro

phyl

axis

Lig

hts

pee

d

Sir

oN

iti-

han

dpie

ceSir

ona,

Bre

iten

bac

h,G

erm

any

Low

torq

ue

5va

lues

All

syst

ems

Ple

ase

no

te,th

atso

me

of

thes

em

oto

rsar

ed

istr

ibu

ted

inso

me

cou

ntr

ies

un

der

dif

fere

nt

nam

esan

db

yd

iffe

ren

td

istr

ibu

tors

.nC

om

bin

edw

ith

elec

tric

alro

ot

can

alle

ngth

mea

sure

men

td

evic

e.D

ue

toh

igh

erro

tati

on

alsp

eed

no

tal

lm

oto

rsar

esu

ited

for

use

wit

hL

igh

tspee

d.

Hulsmann et al.

48

Page 20: Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU¨ LSMANN, OVE A. PETERS & PAUL M.H.

Tab

le5.

Bri

efsu

mm

ary

of

inve

stig

atio

ns

com

par

ing

vari

ous

NiT

iin

stru

men

tsre

gar

din

gth

eir

shap

ing

abliti

ty

Auth

or(

s)R

efer

ence

sYea

rN

iTisy

stem

Met

hod

Res

ult

Esp

osi

to&

Cunnin

gham

(273)

1995

Mac

-Files

,han

d&

rota

ryE

xtra

cted

teet

hN

iTisu

per

ior

toK

-Fle

xm

anual

Glo

sso

net

al.

(27

4)

19

95

Lig

hts

pee

d,M

ity

man

ual

Ext

ract

edte

eth

LS

super

ior

toM

ity

man

.an

dK

-Fle

xm

anu

al

Know

les

etal

.(2

75)

1996

Lig

hts

pee

dE

xtra

cted

teet

hL

ittl

eor

no

tran

sport

atio

n

Gam

billet

al.

(13

4)

19

96

Mit

y-file

sE

xtra

cted

teet

hSuper

ior

toK

-Fle

xm

anu

al

Cole

man

etal

.(2

76)

1996

Ni–

Ti–

K-fi

les

vs.s

teel

file

sE

xtra

cted

teet

hN

i–T

isu

per

ior

wit

hm

inim

alst

raig

hte

nin

g

Zm

ener

&B

aneg

as(2

77

)1

99

6P

roF

ile

0.0

4R

esin

blo

cks

Super

ior

tou

ltra

son

ics

and

K-fi

les

Ch

an&

Ch

eun

g(2

78

)1

99

6M

ity-

file

sR

esin

blo

cks

Super

ior

toK

-file

s

Thar

uniet

al.

(279)

1996

Lig

hts

pee

dR

esin

blo

cks

Super

ior

toK

-file

s

Sh

ort

etal

.(2

25

)1

99

7P

roF

ile

0.0

4,

Lig

hts

pee

d,M

cXim

Ext

ract

edte

eth

All

super

ior

toF

lex-

R

Thom

pso

n&

Dum

mer

(103,104)

1997

Lig

hts

pee

dR

esin

blo

cks

Min

imal

tran

sport

atio

n

Thom

pso

n&

Dum

mer

(280,281)

1997

NT

Engin

e,M

cXim

Res

inblo

cks

Min

imal

tran

sport

atio

n

Thom

pso

n&

Dum

mer

(99,100)

1997

Pro

File

0.0

4,

seri

es2

9R

esin

blo

cks

Lit

tle

tran

sport

atio

n

Bry

ant

etal

.(9

7,9

8)

19

98

Pro

File

0.0

4w

ith

ISO

tips

Res

inb

lock

sL

ittl

est

raig

hte

nin

g,

som

ezi

ps

Cole

man

&Sve

c(2

82)

1997

NiT

i-K

-Files

vs.st

eelfile

sR

esin

blo

cks

NiT

isi

g.

less

stra

ighte

nin

g,

bet

ter

cente

ring

Thom

pso

n&

Dum

mer

(174)

1998

Mit

yR

oto

,N

avifl

exR

esin

blo

cks

No

dif

fere

nce

,litt

lest

raig

hte

nin

g,m

any

ledges

Thom

pso

n&

Dum

mer

(105,106)

1998

Quan

tec

Ser

ies

2000

Res

inblo

cks

More

aber

rati

ons

by

larg

erin

stru

men

ts

Kav

anag

h&

Lum

ley

(283)

1998

Pro

File

0.0

4&

0.0

6E

xtra

cted

teet

hN

odif

fere

nce

,litt

leor

no

tran

sport

atio

n

Shad

idet

al.

(224)

1998

Lig

hts

pee

dE

xtra

cted

teet

hSuper

ior

toF

lex-

R

Sch

afer

&F

ritz

ensc

haf

t(1

94

)1

99

9H

ER

O6

42

Res

inb

lock

sH

ER

O6

42

super

ior

toP

roF

ile

0.0

4su

per

ior

toK

-Fle

xofile

s

Pro

File

0.0

4

Bry

ant

etal

.(1

75)

1999

Com

bin

atio

no

f

Pro

File

0.0

4an

d0

.06

Res

inb

lock

sA

deq

uat

esh

ape

wit

hlitt

lest

raig

hte

nin

g

Ott

ose

net

al.

(28

4)

19

99

Pro

File

0.0

4vs

.N

avifl

exE

xtra

cted

teet

hL

ittl

etr

ansp

ort

atio

n,

no

dif

fere

nce

Mechanical preparation of root canals

49

Page 21: Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU¨ LSMANN, OVE A. PETERS & PAUL M.H.

Tab

le5.

Conti

nued

Auth

or(

s)R

efer

ence

sYea

rN

iTisy

stem

Met

hod

Res

ult

Ku

met

al.

(28

5)

20

00

Pro

File

0.0

&G

TR

ot.

vs.

stee

lfile

sR

esin

blo

cks

Ni–

Tisu

per

ior

toK

-Fle

xofile

s

Jard

ine

&G

ula

biv

ala

(28

6)

20

00

McX

IME

xtra

cted

teet

hE

qu

alto

Fle

xofile

sm

anu

al

Pro

File

0.0

4E

xtra

cted

teet

hE

qu

alto

Fle

xofile

sm

anu

al

Thom

pso

n&

Dum

mer

(101-1

02)

2000

HE

RO

642

Res

inblo

cks

Few

aber

rati

ons

Gri

ffith

set

al.

(17

6)

20

00

Quan

tec

LX

Res

inb

lock

sO

ute

rw

iden

ing

in5

5–8

0%

Gri

ffith

set

al.

(17

7)

20

01

Quan

tec

SC

Res

inb

lock

sSev

ere

aber

rati

on

saf

ter

inst

r.n

o.7

,o

ute

rw

iden

ing

Glu

skin

etal

.(2

87

)2

00

1G

TR

ota

ryvs

.F

lexo

file

sE

xtra

cted

teet

hL

ittl

etr

ansp

ort

atio

n,

super

ior

toF

lexo

file

s

Ber

tran

det

al.

(288)

2001

HE

RO

642

Ext

ract

edte

eth

Lit

tle

tran

sport

atio

n,

super

ior

tost

eelhan

dfile

s

Pet

ers

etal

.(1

40

)2

00

1L

igh

tspee

d,P

roF

ile

0.0

4,

GT

Ro

tary

Ext

ract

edte

eth

Lit

tle

tran

spo

rtat

ion

Huls

man

net

al.

(17

8)

20

01

HE

RO

64

2vs

.Q

uan

tec

SC

Ext

ract

edte

eth

No

dif

fere

nce

,litt

leo

rn

otr

ansp

ort

atio

n

Cal

ber

son

etal

.(2

89

)2

00

2G

TR

ota

ryR

esin

blo

cks

Lit

tle

tran

spo

rtat

ion

Ber

gm

ans

etal

.(2

90

)2

00

2L

igh

tspee

dvs

.G

TR

ota

ryE

xtra

cted

teet

hN

od

iffe

ren

ce,litt

letr

ansp

ort

aio

n

Sch

afer

&L

ohm

ann

(187)

2002

Fle

xMas

ter

vs.K

-Fle

xofile

Res

inblo

cks

Min

imal

tran

sport

atio

n,

super

ior

toK

-Fle

xofile

s

Sch

afer

&L

ohm

ann

(188)

2002

Fle

xMas

ter

vs.K

-Fle

xofile

Ext

ract

edte

eth

Fle

xMas

ter

super

ior

toK

-Fle

xofile

s

Ver

sum

eret

al.

(17

9)

20

02

Pro

File

0.0

4vs

.L

igh

tspee

dE

xtra

cted

teet

hN

od

iffe

ren

ce,litt

leo

rn

otr

ansp

ort

atio

n

Huls

man

net

al.

(18

0)

20

03

Fle

xMas

ter

vs.H

ER

O6

42

Ext

ract

edte

eth

No

dif

fere

nce

,litt

leo

rn

otr

ansp

ort

atio

n

Wei

ger

etal

.(2

91)

2003

Fle

xMas

ter

vs.L

ights

pee

dE

xtra

cted

teet

hL

ittl

etr

ansp

ort

atio

n,

Lig

hts

pee

dsu

per

ior

toF

M

Hub

sch

eret

al.

(14

3)

20

03

Fle

xMas

ter

Ext

ract

edte

eth

Lit

tle

tran

spo

rtat

ion

Sch

afer

&F

lore

k(1

89

)2

00

3K

3R

esin

blo

cks

Lit

tle

tran

spo

rtat

ion

,su

per

ior

toK

-Fle

xofile

s

Sch

afer

&Sch

lin

gem

ann

(19

0)

20

03

K3

Ext

ract

edte

eth

Lit

tle

tran

spo

rtat

ion

,su

per

ior

toK

-Fle

xofile

s

Pet

ers

etal

.(2

92

)2

00

3P

roT

aper

Ext

ract

edte

eth

Lit

tle

tran

spo

rtat

ion

Ber

gm

ans

etal

.(2

93

)2

00

3P

roT

aper

vs.

K3

Ext

ract

edte

eth

Lit

tle

tran

spo

rtat

ion

Hulsmann et al.

50

Page 22: Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU¨ LSMANN, OVE A. PETERS & PAUL M.H.

However, in a comparative study of a low-torque

(o1 N/cm) and a high-torque (43 N/cm) motor

with used rotary NiTi instruments the former yielded

significantly higher resistance to cyclic fatigue com-

pared with usage at high torque (268).

It should be noted in this context that systematic

comparative studies of different endodontic motors are

missing. This is also at least in part because of current

norms that do not mirror the clinical situation for

rotary instruments and the scarcity of adequately

controlled experiments.

Studies on root canal preparation using NiTisystems

Cleaning ability

Studies on various NiTi instruments (Table 5) in the

last years have focused on centring ability, maintenance

of root canal curvature, or working safety of these new

rotary systems; only relatively little information is

available on their cleaning ability. It should be

mentioned that the term ‘canal cleaning’ is used in this

review for the ability to remove particulate debris from

root canal walls with cleaning and shaping procedures.

This property usually has been determined using

scanning electron micrographs (for a review see (13)).

For example, the results for Quantec instruments

were clearly superior to hand instrumentation in the

middle and apical third of the root canals with the best

results for the coronal third of the root canal. In many

specimens only a thin smear layer could be detected

with many open dentinal tubules (81). Kochis et al.

(269) could find no difference between Quantec and

manual preparation using K-files. Peters et al. (270) and

Bechelli et al. (271) described a homogeneous smear

layer after Lightspeed preparation. In a further study no

differences between Quantec SC and Lightspeed could

be found (181), both systems showed nearly complete

removal of debris but left smear layer in all specimens.

In the majority of specimens in both groups cleanliness

was clearly better in the coronal than in the apical part

of the root canals. The results are comparable with

those in previous studies (178–180). However, in the

latter studies EDTA was used only as a paste during

preparation but a final irrigation with a liquid EDTA

solution may increase the degree of cleanliness. In

contrast, FlexMaster, ProTaper and HERO 642

showed nearly complete removal of debris, leaving

Tab

le5.

Conti

nued

Auth

or(

s)R

efer

ence

sYea

rN

iTisy

stem

Met

hod

Res

ult

Huls

man

net

al.

(18

1)

20

03

Lig

hts

pee

dvs

.Q

uan

tec

SC

Ext

ract

edte

eth

No

dif

fere

nce

,litt

leo

rn

otr

ansp

ort

atio

n

Bra

un

etal

.(2

94)

2003

Pro

File,

Fle

xMas

ter.

K-F

iles

Ext

ract

edte

eth

Pro

File

&F

lexM

aste

rsu

per

ior

toK

-file

s

Vel

triet

al.

(29

5)

20

04

GT

Ro

tary

vs.

Pro

Tap

erE

xtra

cted

teet

hN

od

iffe

ren

ce,litt

leo

rn

otr

ansp

ort

atio

n

Sch

afer

&V

lass

is(1

91

)2

00

4P

roT

aper

vs.

RaC

eE

xtra

cted

teet

hR

aCe

sign

.bet

ter

than

Pro

Tap

er

Sch

afer

&V

lass

is(1

92

)2

00

4P

roT

aper

vs.

RaC

eR

esin

blo

cks

RaC

esu

per

ior

toP

roT

aper

Paq

ue

etal

.(1

70

)P

roT

aper

vs.

RaC

eE

xtra

cted

teet

hN

od

iffe

ren

ce,litt

leo

rn

otr

ansp

ort

atio

n

Mechanical preparation of root canals

51

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only a thin smear layer with a relatively high percentage

of specimens without smear layer (170, 180). Prati et al.

(272) found no difference between stainless-steel K-

files and K3, HERO 642, and RaCe NiTi instruments.

Following preparation with FlexMaster and K3,

Schafer & Lohmann (188) and Schafer & Schlinge-

mann (190) found significantly more debris and smear

layer than after manual preparation with K-Flexofiles,

although these differences were not significant for the

middle and apical thirds of the root canals. RaCe

performed better when compared with ProTaper

(192). They discovered uninstrumented areas with

remaining debris in all areas of the canals irrespective of

the preparation technique with the worst results for the

apical third. This is in agreement with the results of

several earlier studies on post-preparation cleanliness

(63, 178–181, 193, 272). These findings underline the

limited efficiency of endodontic instruments in clean-

ing the apical part of the root canal and the importance

of additional irrigation as crucial for sufficient desinfec-

tion of the canal system. Compared with results of a

similar study using ProFile NiTi files, Schafer &

Lohmann (188) found FlexMaster to be superior to

K-Flexofiles in terms of debris removal and concluded

that different rotary NiTi systems vary in their debris

removal efficiency, which is possibly because of differ-

ing flute designs. The comparison of previous studies

on instruments with and without radial lands (ProFile,

Lightspeed, HERO 642) (178–181) confirms the

finding that radial lands tend to burnish the cut dentine

onto the root canal wall, whereas instruments with

positive cutting angles seem to cut and remove the

dentine chips.

Nevertheless, it must be concluded from the pub-

lished studies that the majority of NiTi systems seems

unable to completely instrument and clean the root

canal walls.

Straightening

Results of selected studies on shaping effects of rotary

NiTi systems are presented in Table 5. The vast

majority of these studies uniformly describe good or

excellent maintenance of curvature even in severely

curved root canals. This is confirmed by several

investigations of post-operative cross-sections showing

good centring ability with only minor deviations from

the main axis of the root canal (134, 224, 226, 228,

274, 278, 284, 296–300).

It has been further demonstrated that adequate

preparation results can be obtained with NiTi instru-

ments, even by untrained operators and inexperienced

dental students (287, 301–303).

Safety aspects

Major concern has been expressed concerning the

incidence of instrument fractures during root canal

preparation (194). Two modes of fractures can be

distinguished: torsional and flexural fractures (304,

305). Flexural fractures may arise from defects in the

instrument surface and occur after cyclic fatigue (306).

The discerning feature is believed to be the macro-

scopic appearance of fractured instruments: those with

plastic deformation have fractured because of high

torsional load while fragments with no obvious signs

are thought to have fractured because of fatigue (304).

A summary of factors that may influence instrument

separation is presented in Table 6. Anatomical condi-

tions such as radius and angle of root canal curvature,

the frequency of use, torque setting and operator

experience are among the main factors, while selection

of a particular NiTi system, sterilization and rotational

speed, when confined to specific limits, seem to be less

important (307–338).

Further aspects of working safety such as frequency of

apical blockages, perforations, loss of working length

or apical extrusion of debris until now have not been

evaluated systematically. From the studies described so

far it may be concluded that loss of working length and

apical blockages in fact do occur in some cases, while

the incidence of perforations seems to be negligible.

The amount of apically extruded debris has been

evaluated in three studies and reported to be not

significantly different to hand preparation with Ba-

lanced force motion or conventional rotary systems

using steel files (13, 153, 154).

Working time

The majority of comparative studies presents some

evidence for shorter working times for rotary NiTi

preparation when compared with manual instrumenta-

tion. NiTi systems using only a small number of

instruments, for example ProTaper, completed pre-

paration clearly faster than systems using a large

number of instruments (e.g., Lightspeed). It should

be noted that reported working times for hand

Hulsmann et al.

52

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Tab

le6.

Sum

mar

yof

refe

rence

sin

vest

igat

ing

the

influen

ceof

vari

ous

fact

ors

on

def

orm

atio

nan

dse

par

atio

nof

NiT

iin

stru

men

ts

Auth

or(

s)Yea

rR

efer

ence

sA

nal

yzed

fact

or

Ni–

Tisy

stem

Met

hod

Influen

ce

Silva

ggio

&

Hic

ks

19

97

(30

7)

Ste

riliza

tio

nP

roF

ile

0.0

41–1

0cy

cles

Tors

ion

alte

stN

o

Pru

ett

etal

.1997

(308)

Can

alcu

rvat

ure

&ro

t.

spee

d

Lig

hts

pee

d30–6

01

curv

ature

s,Sim

ula

ted

canal

sYes

2–5

mm

radiu

san

d7

50

,

13

00

,2

00

0r.

p.m

.

Yes

No

Hai

kelet

al.

19

98

(30

9)

NaO

Clas

irri

gan

tD

iffe

ren

tsy

stem

sP

repar

atio

nw

ith

/

wit

hout

NaO

Cl

Tors

ion

alte

stN

o

Miz

eet

al.

1998

(310)

Ste

riliza

tion

Lig

hts

pee

dN

o

Man

del

etal

.1999

(311)

Oper

ator

exper

ience

Pro

File

0.0

4an

d0.0

65

oper

ators

Sim

ula

ted

canal

sYes

Bet

ter

resu

lts

in

seco

nd

turn

Bau

man

n&

Ro

th

19

99

30

4O

per

ato

rex

per

ien

ceP

roF

ile

0.0

4Stu

den

tsvs

.

pra

ctit

ioner

s

Sim

ula

ted

canal

sN

o

Gab

elet

al.

19

99

(31

2)

Ro

tati

onal

spee

dP

roF

ile

0.0

416

6vs

.3

33

r.p.m

.E

xtra

cted

teet

hYes

16

6r.

p.m

.w

ith

less

frac

ture

s/dis

tort

ions

Hai

kelet

al.

1999

(313)

Rad

ius

of

curv

ature

in-

stru

men

tta

per

&si

ze

Pro

File

0.0

4an

d0

.06

,

HE

RO

642,

Quan

tec

5an

d1

0m

mra

diu

sF

atig

ue

test

Yes

Ear

lier

frac

ture

wit

hlo

w

rad

ius

Yes

Ear

lier

frac

ture

wit

hin

cr.

size

Yar

edet

al.

19

99

(31

4)

Ste

riliza

tio

n&

sim

ula

ted

clin

ical

use

Pro

File

0.0

65

vs.

10

can

als/

ster

iliz

atio

ncy

cles

Ext

ract

edte

eth

No

Die

tzet

al.

20

00

(31

5)

Ro

tati

onal

spee

dP

roF

ile

0.0

415

0/

25

0/

35

0r.

p.m

.Yes

Les

sfr

actu

res

wit

h

15

0r.

p.m

.

Yar

edet

al.

20

00

(31

6)

Ste

riliza

tio

n&

clin

ical

use

Pro

File

0.0

6N

o

Hilt

etal

.2000

(317)

Ste

riliza

tion

NiT

ifile

s10–4

0cy

cles

,2

auto

clav

esN

o

Mechanical preparation of root canals

53

Page 25: Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU¨ LSMANN, OVE A. PETERS & PAUL M.H.

Tab

le6.

Conti

nued

Auth

or(

s)Yea

rR

efer

ence

sA

nal

yzed

fact

or

Ni–

Tisy

stem

Met

hod

Influen

ce

Bort

nic

ket

al.

2001

(318)

Moto

rP

roF

ile

0.0

4el

ectr

icvs

.ai

rdri

ven

han

dpie

ce

Ext

ract

edte

eth

No

Dau

gh

erty

etal

.

20

01

(31

9)

Ro

tati

onal

spee

dP

roF

ile

0.0

415

0vs

.3

50

r.p.m

.E

xtra

cted

teet

hN

o

Gam

bar

ini

2001

(320)

Moto

rP

roF

ile

0.0

4an

d0.0

6hig

h-

vs.lo

w-t

orq

ue

Use

din

stru

men

tsYes

Low

-torq

ue

favo

rable

Gam

bar

ini

20

01

(32

1)

Fre

qu

ency

of

use

Pro

File

0.0

4an

d0

.06

new

/u

sed

(10�

)

inst

rum

ents

Yes

Ear

lier

frac

t.fo

ru

sed

inst

r.I5

8

Tyg

esen

etal

.2

00

1(3

22

)N

iTisy

stem

Pro

File

0.0

4E

xtra

cted

teet

hN

o

Ni–

TiP

ow

-R0

.04

Yar

edet

al.

20

01

a(3

23

)R

ota

tio

nal

spee

dP

roF

ile

0.0

615

0/

25

0/

35

0r.

p.m

.E

xtra

cted

teet

hYes

15

0r.

p.m

.su

per

ior

to

35

0r.

p.m

.

oper

ator

exper

ien

ce

3oper

ators

wit

h

dif

fere

nt

exper

ience

Yes

torq

ue

20

/3

0/

55

Ncm

No

Yar

edet

al.

2001b

(324)

Moto

rP

roF

ile

0.0

6hig

h-

vs.lo

w-t

orq

ue

Ext

ract

edte

eth

No

Yar

edet

al.

20

02

(32

5)

Ro

tati

onal

spee

dG

TR

ota

ry15

0/

25

0/

35

0r.

p.m

.E

xtra

cted

teet

hN

o

To

rqu

eo

per

ato

r

exper

ien

ce

20

/3

0/

55

Ncm

3

oper

ato

rsw

ith

dif

fere

nt

exper

ience

No

No

Liet

al.

20

02

(32

6)

Ro

tati

onal

spee

d,

han

dlin

gm

od

ean

gle

of

curv

ature

Pro

File

0.0

420

0/

30

0/

40

0r.

p.m

.F

atig

ue

test

Yes

Yes

Pet

ers

&

Bar

bak

ow

2002

(305)

Num

ber

of

rota

tions,

torq

ue,

forc

e,h

and

lin

g

par

amet

ers

sim

ula

ted

can

als

vs.

teet

h

Pro

File

0.0

4P

roF

ile

0.0

4/

15

,

0.0

4/

30

,0

.04/

45

Fat

igu

ete

stYes

Sig

n.m

ore

rot.

tofr

act.

Fo

r0

.04/

15

Hulsmann et al.

54

Page 26: Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU¨ LSMANN, OVE A. PETERS & PAUL M.H.

Tab

le6.

Conti

nued

Auth

or(

s)Yea

rR

efer

ence

sA

nal

yzed

fact

or

Ni–

Tisy

stem

Met

hod

Influen

ce

Yar

ed&

Ku

lkan

i

2002

(328)

Moto

rP

roF

ile

0.0

6A

irm

oto

r,hig

h-

&

low

-&

very

-low

-to

rqu

e

Ext

ract

edte

eth

wit

h

lim

ited

acce

ss

Yes

Ver

ylo

w-t

orq

ue

super

ior

Rola

nd

2002

(329)

Pre

flar

ing

Pro

File

0.0

4C

row

n-d

ow

nvs

.cr

ow

n-

do

wn

1pre

flar

ing

Ext

ract

edte

eth

Yes

Les

sfr

act.

wit

hpre

flar

ing

Zel

ada

etal

.2

00

2(3

30

)R

ota

tio

nal

spee

dro

ot

canal

curv

ature

Pro

File

0.0

4&

0.0

615

0/

25

0/

35

0r.

p.m

.

o3

01/4

301

Ext

ract

edte

eth

No

Yes

All

frac

ture

sin

canal

s.

wit

h4

301

curv

atu

re

Yar

edet

al.

2003a

(331)

Moto

ro

per

ator

exper

i-

ence

Pro

Tap

erhig

h-

vs.lo

w-t

orq

ue

3

oper

ato

rsw

ith

dif

fere

nt

exper

ien

ce

Ext

ract

edte

eth

No

Yar

edet

al.

20

03

b(3

32

)U

sed

vs.n

ewin

stru

-

men

ts

K3

Sim

ula

ted

canal

sYes

Use

din

stru

men

tsfr

actu

re

atlo

wer

angle

san

dto

rque

Mar

tin

etal

.2

00

3(3

33

)R

ota

tio

nal

spee

dan

gle

&ra

diu

sof

curv

ature

Pro

Tap

ervs

.K

315

0/

25

0/

35

0r.

p.m

.

o3

01/4

301

Ext

ract

edte

eth

Yes

Yes

No

influ

ence

of

radiu

s

of

curv

e

O’H

oy

etal

.2003

(334)

Cle

anin

gpro

cedure

sP

roF

ile

1%

NaO

Clvs

.1%

NaO

Cl1

19

%N

aCl

Fat

igue

test

No

Up

to10

cycl

esw

ithout

infl.

Ber

utt

iet

al.

20

04

(33

5)

Pre

flar

ing

torq

ue

Pro

Tap

erF1,F2,S1

&S2

inst

ru-

men

tshig

hvs

.lo

wto

rque

Sim

ula

ted

canal

sYes

Yes

An

kru

met

al.

20

04

(33

6)

Typ

eo

fN

i–T

iin

stru

-

men

t

K3

,P

roT

aper

&P

roF

ile

seve

rely

curv

edca

nal

s

(40

–751)

Ext

ract

edte

eth

No

PT

:6.0

%ofin

str.

frac

ture

d,

PF

:1

.7%

,K

3:2

.1%

;d

iff.

no

tsi

gn

.

Fif

eet

al.

20

04

(33

7)

Fre

qu

ency

of

use

Pro

Tap

erN

ew/

6–8

and

12

–16

roo

tca

nal

s

Ext

ract

edte

eth

Yes

On

lyfo

rS2

and

F2

Bes

tet

al.

20

04

(33

8)

Defl

ecti

on

angle

Pro

File

Var

yin

gd

eflec

tio

nan

gle

sF

atig

ue

test

Yes

Mechanical preparation of root canals

55

Page 27: Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU¨ LSMANN, OVE A. PETERS & PAUL M.H.

instruments as well as for NiTi preparation demonstrate

large variations, indicating a substantial influence of the

operator’s attitude and preparation technique.

The Gottingen studies

Studies on rotary NiTi instruments performed with the

Gottingen experimental design until now have been

performed on the following NiTi systems: Lightspeed,

ProFile 0.04, Quantec SC, FlexMaster, HERO 642,

ProTaper, RaCe, ENDOflash, NiTiTee, K3, GT

Rotary. Some of these systems have been investigated

twice. Mean root canal curvature pre-operatively was

standardized among the groups and ranged between

25.51 and 28.41. All root canals were prepared to size

#45 or at least to the largest file available if no size #45

instruments were available. A paste-type chelator was

used during preparation and irrigation was performed

with 2 mL NaOCl after each instrument.

Cleaning efficacy

Throughout the studies no completely cleaned root

canals could be found regardless of the NiTi system

investigated. Whereas most of the debris was removed

different degrees of smear layer were found in all root

canals. Cleanliness uniformly decreased from the

coronal to the apical third of the root canals, instru-

ments with actively cutting blades showed better

cleanliness than files with radial lands.

Straightening

No significant differences were found between the

different NiTi systems concerning straightening with

exception of more pronounced deviations with Quan-

tec SC, which may be because of the cutting tip of the

files. With regard to the experimental set-up (measure-

ment of the movement of the long axis after super-

imposition of radiographs under a 10-fold

magnification) it seems questionable, whether the

observed amount of straightening really is of any

clinical significance.

Cross-sections

The analysis of the pre- and post-operative cross-

sections revealed that most of the root canals showed an

oval or round cross-section with most of the circum-

ference prepared. Nevertheless, it must be noted that a

noticeable part of the specimens still had unprepared

areas in all thirds of the root canal despite preparation

to size #45. In addition, it was found that NiTi

instruments because of their flexibility had deficiencies

in preparation of oval root canals, since it was not

possible to direct these flexible instruments into the

recesses (137).

Safety

The overall number of procedural incidents such as file

fractures, apical blockages, loss of working length or

perforations was relatively small when compared with

other investigations. Although the operators had been

trained before the studies on a limited number of root

canals (approximately 20 per system) they should be

regarded as inexperienced operators. The maximum

number of fractures was five for Lightspeed, but it

should be noted that most of these investigations were

undertaken with a high-torque motor.

Working time

The results for working time differed widely reflecting

operators’ experience. Probably, working time is the

parameter with the largest inter-individual variations in

any preparation technique. Nevertheless, working time

was shorter than for manual preparation or most

automated systems.

The Cardiff studies

The results of the Cardiff studies are summarized

briefly in Table 5. These studies demonstrated an

impact of angle and radius of the curvature on

preparation outcome. Again, overall there were minor

differences between the different NiTi systems with

exception of the Quantec SC instruments showing a

high number of procedural problems such as perfora-

tions, zipping and loss of working length.

The Zurich studies

In extracted maxillary molars, ProTaper, ProFile, GT

Rotary, Lightspeed, and FlexMaster prepared root

canals without major shaping errors or procedural

incidents and similar to NiTi hand instruments used in

Balanced force motion (50, 139–142, 292). There

were no (50) or few instrument fractures, even though

Hulsmann et al.

56

Page 28: Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU¨ LSMANN, OVE A. PETERS & PAUL M.H.

inexperienced operators shaped narrow and curved

canals (141, 142). As expected, canal volumes were

significantly larger after preparation. However, mea-

sured canal volumes after shaping ranged from 1 to

about 15 mm3, and amount therefore to only about

0.1% of the volume used to for irrigation (1–2 mL).

Overall, canal transportation was found to be in the

range of 100–200 mm, which is in accordance with

similar studies (293). A new variable, canal ‘thickness’,

allowed to follow canal profiles and to determine the

theoretical depth of insertion of instruments for

subsequent root canal filling. It was found that with

contemporary instruments and sequences, fine plug-

gers and spreaders would be introduced to the 5 mm

level (141, 142). A further variable, the amount of

instrumented radicular wall area, varied among canals,

and less so among NiTi instruments used. Overall, 30–

40% of the canal surface area remained uninstrumen-

ted. In all these experiments, pre-operative root canal

geometry was demonstrated to have a greater influence

on the preparation result than the preparation techni-

ques themselves (139–142). However, an oscillating

instrument produced preparation errors and thinned

root dentine significantly compared with the NiTi

rotary systems tested earlier (143).

The Munster studies

Some newer NiTi rotary systems were tested in

simulated canals in resin blocks as well as in extracted

teeth and the results of these studies are briefly

summarized in Table 5.

ProTaper, HERO 642, K3, ProFile, FlexMaster, and

RaCe respected canal curvature well and were relatively

safe to use (186–194). ProTaper showed more

transportation to the outer aspect of the curvature.

FlexMaster preparations were superior to crowndown

preparation using K-Flexofiles in terms of straighten-

ing, but root canal walls were significantly better

cleaned after manual preparation with K-Flexofiles.

There were only minor differences in terms of working

time and loss of working length. No completely cleaned

canals were found for either technique, although major

debris was removed by all systems, with only different

degrees of smear layer remaining on the root canal

walls. Overall, RaCe performed slightly better than

ProTaper (191, 192); K Flexofiles better than K3 (189,

190). Cleanliness decreased from the coronal to the

apical third of the canals.

Concerning safety of use some systems as ProFile, K3

and RaCe showed a high incidence of instrument

separation. However, as some of these instruments

fractured in plastic blocks, care should be take when

extrapolating these results to the clinic.

Conclusions

As a conclusion it may be stated, that

� the use of NiTi instruments results in less straigh-

tening and better centred preparations of curved

root canals,

� the use of NiTi instruments alone does not result in

complete cleanliness of the root canal walls,

� cleanliness decreases from the coronal to the apical

part of the root canal,

� the use of a paste-type chelator during preparation

does not remove the smear layer completely,

� the use of NiTi instruments with active cutting

blades is superior to instruments with radial lands in

terms of root canal cleanliness,

� when used according to the manufacturers’ guide-

lines NiTi instruments seem to be safe to use,

� the use of instruments with safety tips seems to be

preferable with respect to working safety,

� the use of a special motor with constant speed, low

torque and torque-control is recommended.

Ultrasonics

The first use of ultrasonics in endodontics was reported

by Richman (15). In 1976 Howard Martin developed a

device for preparation and cleaning of root canals and

named this technique as ‘endosonics’. Ultrasonic

devices are driven by magnetostriction or piezoelec-

tricity, resulting in oscillation (25–40 kHz) of the

inserted file which initiates acoustic microstreaming in

the irrigation fluid (339). Initially, it was felt that

ultrasonics allowed root canal preparation to be carried

out concurrently with activated irrigation, because of

cavitation effects (16). However, several studies have

demonstrated that acoustic streaming should be

regarded the main mode of action (92, 340–344).

Shaping

Results of studies concerning preparation quality of

ultrasonic devices in their majority report on unsatisfy-

Mechanical preparation of root canals

57

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ing results, namely frequent zipping and straightening

(13, 54, 57, 63, 88, 117, 241, 247–252, 345–347).

Only few studies have been published reporting good

shaping ability of ultrasonic systems (348–350). Several

reports have presented pictures of longitudinal grooves

in the root dentine following the use of ultrasonically

activated files (13, 54, 88, 351) (Fig. 13).

Cleaning ability

The cleaning and disinfecting capacity of ultrasonics

still is subject of controversy (see also other reviews in

this issue). Several studies have demonstrated enhanced

root canal cleanliness including improved removal of

smear layer compared with conventional irrigation

techniques (352–361) (Fig. 14); other studies have

reported similar results for ultrasonis and conventional

preparation/irrigation (83, 84, 88, 89, 169, 251, 255,

362–365), or even superior performance of manual

techniques (77, 86).

If ultrasonics is used for irrigation purposes care

should be taken to introduce the ultrasonic instrument

and activate the unit to oscillate the file in the irrigant

without touching the root canal walls (360, 361,

366–368).

Working safety

Apical blockages (13, 55, 350), ledging (347), loss of

working length (13, 55), a higher risk of perforations

(13) and increased amount of apically extruded debris

(144, 369) as well as instrument fractures (13, 55, 57,

350, 353, 370) have been described for ultrasonic

preparation.

Working time

Time required for ultrasonic preparation has been

shown to be shorter (64, 376), longer (13, 55, 346,

357, 366), or equal (253) when compared with hand

instrumentation.

In conclusion, the use of an ultrasonic device may be

recommended for passive ultrasonic irrigation but not

for root canal preparation.

Laser

The first use of lasers in endodontics has been reported

by Weichman & Johnson (17). They tried to seal the

apical foramen ex vivo by means of a CO2 laser. Since

then numerous studies have been undertaken with

various types of lasers: Nd : YAG-, KTP-, Er : YAG-,

(Ho) : YAG-, XeCl-Excimer-, argon- and free-electron

lasers. Laser irradiation has been demonstrated to be

able to change or modify the structure of dentine,

thereby reducing its permeability (371) and melting or

carbonizing its surface. For some lasers the removal of

debris and smear layer has been reported (372), but it

may be questioned whether it is possible to irradiate the

complete lateral canal walls with currently available

laser systems emitting the light straight ahead (373).

Several investigations have been undertaken to study

Fig. 13. Root canal wall after preparation with anultrasonic system showing heavy longitudinal grooves(original magnification � 250). Reprinted by permissionfrom Quintessence.

Fig. 14. Root canal wall cleanliness following irrigationwith an ultrasonic device and tap water showing goodremoval of debris and smear layer (original magnification� 1000). Reprinted by permission from Quintessence.

Hulsmann et al.

58

Page 30: Mechanical preparation of root canals: shaping goals ... · Mechanical preparation of root canals: shaping goals, techniques and means MICHAEL HU¨ LSMANN, OVE A. PETERS & PAUL M.H.

the sterilization of root canals with different laser types

(for a review see Kimura et al. (373)).

In contrast some concern has arisen over the side-

effects of lasers such as thermal damage to dental hard

tissues resulting in cracks or injury to the surrounding

soft tissues such as ankylosis, cemental lysis and bone

remodelling (374). Moreover, the shaping ability of

lasers in curved root canals seems to be questionable, at

least with the current front-emitting probes.

In conclusion, lasers are recommended by some

authors for disinfection but at present are not suited

for the preparation of root canal systems. The selec-

tion of appropriate irradiation parameters is mandatory,

but these parameters have not yet been defined for

all laser systems. In addition, different tip designs such

as flexible and side-emitting probes need to be

developed.

NIT

The so-called NIT was developed by Lussi et al. (19).

The technique uses a vacuum pump and an electrically

driven piston, generating alternating pressure and

bubbles in the irrigation solution, inside the root canal.

This is expected to enhance the ability of sodium

hypochlorite to dissolve organic pulp tissue. Follow-

ing the cleansing procedure the root canal may

be obturated by the vacuum pump with a sealer

(375–378).

Studies from the Lussi group demonstrated an equal

or even better cleanliness compared with hand instru-

mentation in root canals of extracted teeth (379–382).

In a recent in vivo study 22 teeth (18 patients)

subjected to extraction because of periodontal destruc-

tion were cleansed using the NIT and, following

extraction, investigated under the microscope for

intra-canal residual tissue. The mean percentage of

teeth with tissue remnants and remaining debris in the

coronal third of the root canal was shown to be 34.4%,

55.8% in the middle third, and even 76.6% in the apical

part (383). Additionally, intra-operative problems as

severe pain, underextension and apical extrusion of

sealer or breakdown of vacuum have been reported

(383, 384) (Fig. 15).

In conclusion, as the NIT system is presently not

marketed and long-term observations are missing, it

cannot not be regarded as an alternative to mechanical

root canal instrumentation.

Preparation of oval root canals

In the recent literature few data on preparation of oval

shaped root canals are available. Such cross-sectional

shapes can often be found in the distal root canals of

mandibular molars or in mandibular incisors. In an

investigation of 180 teeth of all groups Wu et al. (385)

detected oval canals in 25% of all sections investigated.

According to the criteria used in studies of Wu et al.

(385, 386) and Wu & Wesselink (387) only teeth with a

bucco-lingual distance at least 1.5 � as long as the

mesio-distal distance (internal long to short diameter

ratio) are defined as oval. Difficult areas for instrumen-

tation and obturation are the buccal and lingual

extensions of these irregular canals (385). Complete

preparation with stainless-steel instruments includes a

high risk of perforating or significantly weakening the

root. On the other hand it seems questionable whether

Fig. 15. (A, B) Root canals surface following cleansingwith the Non-Instrumental Technique of Lussidemonstrating insufficient cleaning ability with lots ofremaining debris and tissue (courtesy of Prof. T. Attin,Gottingen and Prof. A. Lussi, Bern).

Mechanical preparation of root canals

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flexible NiTi instruments allow controlled and com-

plete preparation of such extensions. However, specific

instrumentation motions such as ‘brushing’ have been

recommended to be used with some instruments (see

clinical articles in this issue).

Because of limited efficacy of irrigation in such

recesses, debris and smear layer may accumulate and

remain on these unprepared root canal walls, decrease

the quality of obturation and jeopardize the long-term

treatment success.

In a comparative study of preparation of oval root

canals with three NiTi systems, preparation with

ProFile 0.04 was superior in the apical region compared

with Lightspeed and Quantec SC but in all three parts

of the root canals no significant differences between the

three NiTi systems could be found. The middle and

coronal cross-sections were increasingly irregular and

frequently showed circular bulges, whereas the buccal

and lingual extensions of the oval root canals often

remained unprepared (Fig. 16A, B). All three systems

performed relatively poorly in these two sections of the

root canals probably because of their flexibility fre-

quently not allowing the operator to force them into

the lateral extensions. The total amount of non-

instrumented canal areas was rather high (19.2%)

(137). This is in accordance with the results of a

previous investigation by Wu & Wesselink (385), who

following preparation of oval canals in mandibular

incisors with the Balanced force technique, reported

uninstrumented extensions in 65% of the canals.

Similarly, three-dimensional rendering of prepared

canals demonstrate large uninstrumented areas de-

pending on pre-operative canal shapes (327).

Superimposing pre- and post-operative cross-sec-

tional root canal outlines of oval canals Weiger et al.

(388) calculated the ratio of prepared to unprepared

outlines. Preparation using Hedstrom files and HERO

642 rotary NiTi preparation showed better results than

Lightspeed preparation. Barbizam et al. (389) con-

firmed these findings in a study on preparation of

flattened root canals in mandibular incisors. They

reported superior results in terms of root canal

cleanliness for the manual crowndown technique using

stainless-steel K-files compared with ProFile 0.04

rotary preparation. Another investigation (137) found

no significant differences concerning root canal cleanli-

ness between three NiTi systems (Lightspeed, Quantec

SC, ProFile 0.04). Cleaning of recesses in oval canals

may be enhanced by use of sonic or ultrasonic irrigation

techniques, which remove debris but do not affect the

smear layer when used with water as the irrigant.

Therefore sodium hypochlorite or chelating agents

such as EDTA and an adequate irrigation sequence

should be selected. When an ultrasonic unit is used for

irrigation, the file is best directed towards the exten-

sions and away from danger zones (390).

Apical size of preparation

The desirable final size of apical preparation remains

controversial. Two main concepts have been proposed.

The first concept aims at complete circumferential

removal of dentine. The traditional rule has been, to

prepare at least three sizes beyond the first file that

binds at working length. Based on findings that the pre-

operative diameter of the apical foramen is approxi-

mately 500–680 mm and the diameter of the root canal

short of the foramen is on average 300–350 mm (391)

Fig. 16. (A, B) Unprepared buccal and lingual recesses inthe distal root of a mandibular molar. The root canal wasshaped using NiTi instruments.

Hulsmann et al.

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apical preparation has been recommended to ISO sizes

#25–35 (44, 209, 392–395). Nevertheless, this con-

cept has been questioned fundamentally: as stated

earlier, histological studies could demonstrate that 15–

30% of the root canal walls remained untouched by

instruments following manual preparation even when the

recommended instrument sizes were used (396, 397).

Weiger et al. (398) in a laboratory study calculated

that enlargement to initial diameter 10.4 mm in molar

palatal and distal root canals and 10.3 mm in mesio-

buccal, mesio-lingual and disto-buccal root canals of

molars would be necessary to achieve complete pre-

paration of the canal circumference in 78% and 72% of

the canals, respectively. Preparation to initial diame-

ter10.6 mm would result in 95% of the cases prepared

completely, but included a high risk of perforations.

Several comparative investigations of pre- and post-

operative cross-sections of mesio-buccal root canals in

curved mandibular molars resulted in 3 to 18 out of 25

specimens with more than 25% of the diameter left

unprepared following preparation with different rotary

NiTi systems to size #45 (170, 171, 178–183).

The exactness in determination of the ‘first file that

binds’ depends on the degree of pre-flaring and the

type of instrument used. Following pre-flaring larger

instrument sizes can be inserted on working length

(difference: one ISO size); larger Lightspeed instru-

ments than K-files could be inserted. When Lightspeed

with pre-flaring was compared with K-files without pre-

flaring the difference between these techniques in-

creased to three ISO sizes (399).

Wu et al. (400) could detect no difference between K-

files and Lightspeed in determination of pre-operative

apical diameter. They could demonstrate that in 75% of

the root canals the instrument had contact on the canal

wall only on one side, in 25% the instrument tip had no

contact with the canal wall at all.

Kerekes & Tronstad (401) in histomorphometric

studies investigated the smallest file size necessary to

prepare a round canal diameter in mesio-buccal root

canals of mandibular molars. In 12 out of 19 root canals

final preparation sizes of #40–55 were necessary to

achieve this goal.

Following preparation with GT Rotary instruments

to apical sizes 0.06/20 or 0.06/40 in the first group

with smaller apical preparation diameter significantly

more debris was found than after extended preparation

(402). Similar findings were reported by Peters &

Barbakow (403) following preparation with ProFile or

Lightspeed instruments showing more effective re-

moval of the smear layer after larger preparation with LS

instruments. The technique using the largest final apical

file (i.e., Balanced force) produced cleaner apical areas

in curved canals than techniques using smaller final

apical instruments (stepback, crowndown pressureless)

(80). Improved delivery of irrigants is thought to be the

main benefit of larger apical preparation sizes (404).

In contrast, in a comparative study of five preparation

techniques with the size of the final apical file varying

from #25 (stepback technique with stainless-steel files)

to #30 (ultrasonics), #35 (stepback, NiTi files; Canal

Master U) or #40 (Balanced force) no differences in

terms of remaining soft tissue, predentine or debris

were detected (405).

The second concept aims to keep the apical diameter

small and refers to Schilder’s demand to keep the apical

preparation as small as practical (1, 2). This concept for

apical preparation includes scouting of the apical third,

establishing apical patency with a size #10 instrument

passively inserted 1 mm through the foramen, gauging

and tuning the apical third and finally finishing the

apical third at least to size #20. Corresponding to this

technique GT instruments (Dentsply Tulsa Dental,

Tulsa, OK, USA) in their original sequence included

four instruments for apical finishing all of these with

size #20 tips but varying tapers. Similarly, ProTaper

Finishing instruments have apical diameters ranging

from 0.20 to 0.30 mm.

The influence of final apical preparation size has been

examined in two long-term studies on treatment

outcome. Whereas Strindberg (162) reported on a

poorer prognosis for larger apical preparation, Kerekes

& Tronstad (165) found similar results for apical

preparation to ISO sizes 20–40 and 45–100. Card et al.

(406) in vivo could demonstrate a significantly

increased reduction of intra-canal bacteria after apical

enlargement to larger sizes with NiTi instruments.

Based on a review of the literature Friedman recom-

mended larger apical preparation sizes in combination

with abundant irrigation and use of a calcium hydro-

xide dressing (407).

Impact of root canal preparation on thereduction of intra-canal bacteria

While the antimicrobial effect of canal preparation is

reviewed in more detail elsewhere in this issue, it is well

known that canal shaping and cleaning occur concur-

Mechanical preparation of root canals

61

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rently during mechanical preparation. In fact, in their

classical study Bystrom & Sundqvist (408) using an

anaerobic bacteriological technique demonstrated that

mechanical enlargement with sterile saline as an irrigant

was able to reduce the number of microorganisms in

the root canal system significantly from initially 102 to

more than 108 by 100–1000-fold, but could not

predictably achieve bacteria-free root canals. Even

combinations of mechanical preparation and antibac-

terial irrigants were not able to eliminate all bacteria

from root canals (408–412), demonstrating the limited

antibacterial effect of mechanical preparation.

In a clinical study in 23 teeth with apical period-

ontitis, Ørstavik et al. (413) following stepback

preparation and irrigation with sterile saline could yield

positive cultures in 14 of the teeth at the end of the first

appointment. Following a 1-week medication with

calcium hydroxide this number was reduced to eight

teeth. At the end of the second appointment bacteria

could be detected in two root canals. Although root

canals prepared to size #35 or 40 at the end of the first

appointment tended to harbor more bacteria than

canals prepared to size #45 or more, statistical analysis

did not reveal any significance of preparation size on

reduction of bacteria.

Yared & Bou Dagher (414) in an in vivo investigation

in 60 single-rooted teeth with apical periodontitis

found no significant difference in terms of the

reduction of bacteria following preparation to size

#25 or 40, respectively. One percent sodium hypo-

chlorite was used as irrigant. Nevertheless, bacterial

counts were reduced significantly in both groups when

compared with the initial number of microorganisms.

Coldero et al. (415) instrumented palatal root canals

of maxillary molars using sodium hypochlorite (4%)

and EDTA as irrigants. There was no significant

difference in reduction of intra-canal bacteria following

crowndown preparation with GT Rotary to size 0.04/

35 and crowndown with GT Rotary to 0.04/20

followed by stepback to 0.04/35. With both techni-

ques the majority of the root canals (15/16 and 13/16,

respectively) were rendered bacteria free.

Manual instrumentation using NiTi-Flex instru-

ments to size #40 with 0.02 taper, manual instrumen-

tation using GT Rotary to size 0.12/20 and automated

preparation using ProFile 0.06/30 – all techniques

used with sterile saline as an irrigant – resulted in 94.2–

99.6% reduction of intra-canal bacteria with no

statistical difference between the groups (416).

Dalton et al. (417) in a clinical study of 48 teeth

with apical periodontitis could find no difference

between steel files and NiTi instruments in terms of

reduction of bacteria but reported increasing bacterial

reduction with increasing instrument size. Neverthe-

less, it was not possible to achieve bacteria-free root

canals predictably. This was confirmed by a similar

study on NiTi ProFile 0.04 instruments: Shuping et al.

(418) reported on decreasing numbers of intra-canal

bacteria with increasing instrumentation sizes. Addi-

tional use of 1.25% sodium hypochlorite resulted

in 61.9% bacteria-free canals, a calcium-hydroxide

dressing increased this figure to 92.5% of the canals.

Using ProFile 0.04 and 1% sodium hypochlorite in a

clinical study on 40 teeth with apical periodontitis

100% of cuspids and bicuspids and 81.5% of molar

canals could be rendered bacteria free after the first

appointment.

Continued preparation with Lightspeed instruments

to larger sizes resulted in an improvement to 89%

bacteria-free canals after this second appointment with

the difference between the techniques not being

significant (418). Manual preparation using NiTiflex

instruments (size #40) in an alternated rotary motions-

technique or automated GT Rotary NiTi instruments

(0.12/20) with 5% sodium hypochlorite as an irrigant

both significantly reduced the number of viable bacteria

(60.3–78.4% reduction) but failed to render root canals

bacteria free. Additional irrigation with 10% citric acid

or 2% chlorhexidine did not result in significant

improvement. In the control group instrumentation

and irrigation with sterile saline resulted in a 38.3%

reduction of bacteria (419). Between manual prepara-

tion using K-files or K-Nitiflex files in a stepback

technique or K-reamers in a standardized technique no

significant differences could be found in reduction of

bacteria, although all techniques considerably reduced

their number (420).

Rollinson et al. (421) compared the removal of

radioactively labeled bacteria with two different rotary

NiTi preparation techniques. Preparation with Pow-R

instruments to size #50 resulted in less remaining

bacteria than preparation with GT Rotary and ProFile

to size #35.

In contrast, Ørstavik et al. (422) in a multivariate

analysis of the outcome of endodontic treatment in 675

roots in 498 teeth could not find apical extension (i.e.

size of final reamer) or point size were among the

factors influencing treatment outcome.

Hulsmann et al.

62

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In summary, the reduction of intra-canal bacteria will

be mainly because of the antibacterial effects of the

irrigants (and medications) and only partially because

of instrumentation of root canal systems. Mechanical

instrumentation will remove a certain amount of

infected tissue and dentine from the root canal and

facilitate sufficient application of irrigants. Although

there seems to be some evidence that larger apical

preparation sizes result in the reduction of intra-canal

bacteria, the significance of the extent of final apical

preparation size remains to be clarified. NiTi instru-

ments are able to enlarge even curved root canals to

sizes not routinely attainable with steel files but there is

no clear evidence that this automatically results in

improved disinfection.

Impact of root canal preparation ontreatment outcome

The impact of root canal preparation on treatment

outcome recently has been reviewed extensively by

Friedman (407) and Kirkevang & H�rsted-Bindslev

(423) previously in this journal. In summary, Friedman

reported on conflicting results for final apical prepara-

tion size and found only one clinical study favouring a

certain preparation technique (standardized technique

instead of serial preparation) with respect to treatment

outcome.

Peters et al. (424) in a retrospective study of 268

clinical cases with 661 roots after a mean observation

time of 27.1 ( � 9.6) months could not find a

difference in treatment outcome between three NiTi

preparation techniques (Lightspeed, ProFile 0.04, GT

Rotary). It should be noted that only the two first

techniques were used with the same obturation

technique (lateral condensation with GP and AH 26).

Petiette et al. (51) in a 1-year recall study comprising 40

cases reported a significantly better success rate for

teeth prepared with NiTi hand files than with stainless-

steel K-files by dental students. They conclude that

better maintenance of original canal shape led to a

better prognosis. However, Ørstavik et al. (422) could

not verify an influence of final preparation size on

treatment outcome.

Conclusions

Because of the methodological problems described

above and limited clinical and scientific evidence

conclusions on root canal preparation should be drawn

with utmost caution:

� Mechanical preparation of the root canal may result

in a significant reduction of bacteria but will not

reproducibly leave bacteria-free root canals.

� Mechanical preparation leaves a root canal wall

covered with debris and smear layer if not accom-

panied by abundant irrigation with appropriate

solutions.

� Mechanical preparation of the root canal must be

assisted and completed by intense disinfection

protocols using appropriate irrigants and intra-

canal medicaments.

� Preparation technique and instruments and final

preparation size have to be defined individually for

each root canal system.

� The use of NiTi instruments facilitates preparation,

especially of curved root canals.

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